Unable to securely connect to persistent subscription on Follower node

Hello,
I’m using .NET Client version 5.0.12 to connect to a 3 node cluster on server version 21.10.0.
I’m using TCP connection and setting UseSslConnection with validateServer = true.
Also setting PerformOnAnyNode.
I can connect to any individual node and publish to streams without issue, which leads me to believe my certs are set up correctly.
I can connect to a persistent subscription on the Leader node.
But when I try to connect to a sub on the Follower nodes, it immediately disconnects. Verbose logging shows “The remote certificate is invalid according to the validation procedure.” If I set validateServer = false it works on all nodes.

Can’t figure out why validateServer is fine except for on persistent subs on Follower nodes. Any ideas on what is happening here?

Updating the client to v21.2.2 solves the issue.
A somewhat related question, then. Is client v21.2.2 fully backwards compatible with server v4.0.1? I have to deal with some of those old servers that can’t be immediately updated. Everything looks fine in my initial tests, just trying to avoid any surprises.

we have backwards compat with V5 , it is not guaranteed with V4 .