Can Probezeit mess up my citizenship application?

I would ask the authority that processes your application. If you ever get an answer, please come back and post it here, for the benefit of future readers!

But if I were you, I would not apply in such a situation (and give them a chance to reject the application on a such formality). Surely it is not a big deal to wait another six months and apply then!

One should know that requirements for citizenship are generally stated in the minimum terms. Like one has to get at least 60% on the citizenship test and the B1 English test. This does not mean they are guaranteed to be accepted even if they meet all of the minimum requirements. It means that they definitely won’t be accepted if any fall short. In the end they weigh everything together. One of the most important things is finances; looking at jobs, savings, property, debts and expenses. That one has worked steadily for the last years is totally undermined by them being unemployed, even if not strictly their own fault. Even if not on any kind of social assistance (which is an instant fail criteria) then one should have what looks like good prospects to continue to work. Not enough to just be presently employed if a job is planned to end no matter what the reason. Much better to wait and get a new job in such a situation, and minimally keep it past any trial period, to give them the reassurance they want. Otherwise one might get a rejection - with the possibility to apply again in the future when they are employed. But already having a rejection is a kind of red flag. I would always say one should have patience and wait until they are employed without a termination date before applying. It might even be able to be sold as a positive note that one had to get a new job because of such a situation but managed to do it.

I would ask the authority that processes your application. If you ever get an answer, please come back and post it here, for the benefitof future readers!
But if I were you, I would not apply in such a situation (and give them a chance to reject the application on a such formality). Surely it is not a big deal to wait another six months and apply then! - @beppi

It is for me, I want to apply as soon as possible.

@Trabantlover Well, then, you decide yourself what you do and which risk (of rejection) you can accept!