Sorry to be the bearer of bad news, but I have the same problem with my Google Nest Wifi Pro 6e 3-node setup. My two satellite nodes drop offline randomly for random lengths of time, making the mesh unusable. It's apparently also a very well known issue with Google Nest Wifi Pro systems. Google also doesn't seem to have a good understanding of the issue. I say that because for as long as this problem has existed, if they understood what the issue is, there would be an actual fix, and not the hand-waving exercises they have asked community members to perform, myself included.
I'd return my three nodes for a refund and buy another brand's mesh system if I could, but because I'm outside of the return/exchange window, I'm stuck, unless I want to throw more cash at the problem.