Clusterhat wont work anymore

hi

I recently got a Cluster HAT v2.4 and so far it worked well.

The Raspberry Pi Zeros and the PI 3b + that I used for it

also worked without problems.

But since 2-3 days ,the Zeros are no longer displayed in the network.

The first thing I suspected was the operating system of the Zeros, but they boot up without any problem.

I also see the Pi 3 B + and can access it as ususal.

I replaced the USB cable that came with it, but nothing.

if someone could help me with this. That would be great.

Sorry for my bad english.