My desktop wallet is fully synchronized, but from today, when I open it, it stays on 0 connections, I do not know why.
Mine also does that from time to time. I just leave it open until it decides it wants to connect to some peers. I have already added all the available nodes but still run int the 0 connections sometimes. It always picks up one or two and gets me syncing eventually. I have deleted the blocks and chainstate folders and am currently resyncing from 8 peers.
I had the same issue yesterday. No connections after a few hours, nodes added. Rebooting my router did the trick. I think it might be for one of two reasons:
1. The snowgem port in the router crashes, everything else doesn't. Unlikely
2. The snowgem clients "don't like" your IP when they don't see you for a while.