Unchecking "disable network timeouts" does not solve the problem.
I've a bad wifi connection and disruptions occur several times a day. This makes me regularilly loose ranks when I'm not available to reconnect manually (=open a new client with the same track) just before the end of a puzzle.
If it could help:
When I've a permanent disconnection, if I open a new client, the computer reconnects for this client.
After some time (several minutes), several (not all) other clients do reconnect too.
It's like if a new foldit session also reconnects many existing clients but not all of them (may be the oldest ones doesn't reconnect, I'm not sure).