SSL connection fail to one server

Hello,

Very happy user of VHere since... a long time. We are using encrypted connections to our VHere servers, and client certificates. We manage our own CAs.

Since a few weeks ago, SSL connections to one server fail without obvious (for us)  reasons. We had a certificate rotation for the related CA, so there may be something in this direction. We have disabled the client certs for this server (sslClientCerts=0), to limit the search for the problem. 

Here is a (short) log, client-side :

2024-02-21 10:41:01 INFO  :VirtualHere Client 5.5.7 starting (Compiled: Dec 11 2023 11:31:52)
2024-02-21 10:41:01 INFO  :Client OS is Windows 10 (build 19045), 64-bit edition   
2024-02-21 10:41:01 INFO  :Using config at C:\Users\User\AppData\Roaming\vhui.ini  
2024-02-21 10:41:01 INFO  :IPC available at \\.\pipe\vhclient  
2024-02-21 10:41:01 INFO  :Using SSL CA File C:\Users\Public\Documents\CAs.pem  
2024-02-21 10:41:02 INFO  :Using ClientSSLCert at C:\Users\User\Documents\VirtualHere\machine.pem  
2024-02-21 10:41:06 INFO  :Error -0x4380 during SSL handshake when connecting to target:7574, RSA - The PKCS#1 verification failed

Server-side, we only get

Wed Feb 21 11:01:15 2024 LOG_ERR Error -0x7780 during SSL handshake, SSL - A fatal alert message was received from our peer

What could be the problem ? Seems to lie around the server certification chain, but we have not found anything weird (which does not mean there is nothing fishy).

Thanks.