As you found out, it is not a matter of which version of the plugin you’re using. If it was, downgrading would have solved your problem. Also, it wouldn’t make sense for the same code to suddenly stop working. Something else has changed in your environment.
Changing to another service is not likely to help, as most hosts have similar security. You mentioned that the TCP port is open. Did you check both the outgoing and incoming sides? (i.e. You must talk to both hosts.)
Another thought is this: When you enter a passphrase it is normally stored for however many minutes you want, or forever, in which case it is stored on a permanent transient. It is still possible that you, or some clean-up plugin, may have cleared all transients, in which case the wallet would be locked again.
In the site where withdrawals stopped, does the coin adapter now appear locked? If so, this would be a different error than the timeouts you were getting before.
In conclusion, please check the following and let me know:
1. If you checked the firewalls on both sides.
2. If the coin adapter is locked on the site where withdrawals have stopped.
with regards