TL;DR:
I read two articles about this, two statements of Uni Cologne and the open letter to form an opinion. My opinion: Either Cologne decision makers need new reading glasses, or they are too biased in order to take a sufficiently critical stance or I am an idiot and misunderstood a lot.

Long version:
Well that doesn’t sound too well. I was curious about the background of this, read abother german news article which covered that and read the open letter "Philosophy for Palestine, which was signed by Professor Fraser. You can read it here:
https://www.philosophyforpalestine.com/

As far as I understood, questioning the state’s Israel’s right to exist can be a crime under german law, also given specific circumstances. (I didn’t take the time to fully understand it. But stuff like calling for violence against Israel is surely highly problematic, while mere critique against atrocities committed by israel military forces should be okay.)

Although there were imo some difficult passages in the open letter, I think it’s overall a clear cry for ceasefire and peace with a focus on sparing the lifes of innocent civilians; thereby stopping a possible genocide as well.

The difficult passages are imo:

• “since the 1948 establishment of Israel as an ethno-supremacist state”
  Even though it’s true that the state was formed for Jews, labeling the whole state as “ethno-supermacists” leaves me with an impression which tries to bring Israel to one level with other ethno-supermacies from the past or present. Of course the old Nazis are the first thing that comes to my mind. But seeing how much violence has been committed against Palestines and how several independent observers report apartheid-like conditions, it’s also hard to completely disagree with this choice of wording.
• “Most importantly, we are all too aware that the countries in which we live and work and to which we pay taxes is funding and abetting one party and one party only in this deeply asymmetric conflict. That party is not the oppressed, but the oppressor.”
  Framing Israel as “the oppressor” is one of the other expressions I find difficult. The history of the conflict between Palestina and Israel is huge and complex and I don’t want to oversimplify things. I am still not sure I’ve understood the most important points. Based on that limited understanding I can see how Israel appears as an oppressor. Some folks at the UN just decided to give land, where one culture was at home most recently, to another bunch of people. Conflict arised and it’s still a hot mess since then.
  However, borders were created and treaties were signed. Are Israelis oppressors now? I think there are good reasons to feel that way and other ones which would disagree with that. And I still don’t have a fucking clue what to make out of that.
  What I think might be problematic here is that labeling Israel as an oppressor would mean that their military reaction as a consequence to the october massacre is not justified. Destroying the organization which committed such atrocities seems like a legitimate reason. Defending your people and ensure that it won’t happen again is not the worst reason to start a war. I am not a fan of this as I see myself more as a pacifist. Nevertheless, from my point of view this doesn’t make one an oppressor.
  But let’s not forget that the history here isn’t that simple.

What I don’t see in this letter though, is what – in my opinion – would be a good reason to deny Professor Fraser the seat as visiting professor with those special honours. She didn’t deny Israel’s right to exist, nor did she call for violence against the state or it’s people. To the contrary, she supports critique of Israel’s severe military retaliations and asks for peace for the sake of innocent lives.

So why the fuck did Cologne still do this?
They made a statement on this, you can read it here:
https://portal.uni-koeln.de/universitaet/aktuell/presseinformationen/detail/absage-der-albertus-magnus-professur-2024 (German)

To sum up their reasons are based on the contents of the open letter:

1. The right of Israel to exist as a state is questioned. (“In diesem Brief wird das Existenzrecht Israels als “ethno-suprematistischer Staat” seit seiner Gründung 1948 faktisch in Frage gestellt.)”
2. The Hamas’ massacre of October 2023 gets downplayed and justified. (“Der Terrorangriff der Hamas auf Israel vom 7.10.2023 wird in rechtfertigender Weise relativiert.”)
3. The letter demands an academic and cultural boycott of Israeli institutions.(“Die Unterzeichner innen rufen zum akademischen und kulturellen Boykott israelischer Institutionen auf.”) Which is especially problematic for Cologne due to their strong ties to those. ("Und natürlich ist es dann schwierig, das in Übereinstimmung zu bringen mit dem Aufruf zum Boykott israelischer Partnerinstitutionen, […] wenn wir gerade als Universität zu Köln so viele Verbindungen zu Partnerinstitutionen in Israel haben.)
4. They see it as irreconcilable with their stance towards this newly escalated conflict. (“Die Aussagen im Brief der Philosoph innen sind jedoch mit den Stellungnahmen der Universität zu Köln zur Situation in Israel und im Nahen Osten vom 09.10. und 22.10.2023 sowie mit unseren intensiven Beziehungen zu israelischen Partnerinstitutionen nicht vereinbar.”)

Regarding the latter they link to their statement about the Hamas massacre:
https://portal.uni-koeln.de/universitaet/aktuell/presseinformationen/detail/stellungnahme-zur-situation-in-israel-und-im-nahen-osten (German)
It’s worth a read to evaluate this whole ordeal. They show compassion for the victims and those close to them. Also, they worry about an escalation of the conflict and about peace in the whole region. At the same time they expect open and civilized discussions about this on their campus.

It’s also worth mentioning that they don’t forbid Professor Fraser to be a visiting professor at all. They “just” deny her the Albertus-Magnus-professorship which would have been a special way of honouring her. This can be found at the top of their first statement I linked here.

My opinion about their reasons:

• Regarding 1: I can’t see that in the open letter, as I’ve established before.
• Regarding 2: It was in no way justified or downplayed. The letter literally says:
  “To focus, as we do here, on the actions of the Israeli state and the unflagging support it receives from the US and its allies, is neither to celebrate violence, nor to equivocate on the value of innocent lives. Civilian deaths, regardless of nationality, are tragic and unacceptable.”
  I can imagine how the sentence after that can be misunderstood:
  “Yet to act as though the history of violence began with Hamas’s attacks on October 7, 2023 is to display a reckless indifference to history as well as to both Palestinian and Israeli lives.”
  But I don’t understand that as downplaying or justification. To the contrary, I think it highlights the complexity and also urgency or interventions in order to stop the violence on all sides.
• Regarding 3: Calling for a boycott of Israeli institutions seems reasonable if you have sufficient reasons to believe that they are crossing ethical lines and must be stopped. We are boycottivg and sanctioning the shit out of russia for their invasion of Ukraine. Having a University chime in in that, which has a lot of ties to Israeli institutions would have a strong symbolic effect. But Cologne doesn’t even need to do that, which I find more important: just because Professor Fraser would support such sanctions, doesn’t mean the whole University will take a 180° turn on that.
• Regarding 4: See above plus: their stance is not “we support every war crime and atrocity commited by Israel”, but to the contrary: they wish for peace and open civilized discussions about this matter. So I don’t see how that would apply here.

My conclusion:
I think those in Cologne who made these decisions are either opportunists or biased, who don’t wish to anger their friends in Israel, or idiots who did not understand the open letter (or even their own statements).
Maybe I am the idiot. Did I get something wrong?

By the way, Professor Fraser will hold the lectures, which she would’ve held in Cologne, elsewhere now. I don’t know where and when, though. If someone of you knows, I would be happy if you could share that info here.