Connection error: TLS handshake failed

[siceff]

Hello everyone,
I encounter an error with OpenVPN (pfsense CE 2.4.2-RELEASE-p1). The OpenVPN server is configured with the wizard, and the authentication is done by the LDAP server. All the certificates (CA and cert) are auto-generated.

All users can connect the OpenVPN client (all on 2.4.4) but after some minutes (from 5 to 120), the client is disconnected with the following error (error on both server log and client log) :

Feb 20 21:35:46 	openvpn 	828 	cp-jcm/31.10.164.192 TLS Error: TLS key negotiation failed to occur within 60 seconds (check your network connectivity)
Feb 20 21:35:46 	openvpn 	828 	cp-jcm/31.10.164.192 TLS Error: TLS handshake failed
Feb 20 21:35:46 	openvpn 	828 	cp-jcm/31.10.164.192 Fatal TLS error (check_tls_errors_co), restarting 

Maybe I need to post more details, but could you tell me on which direction I need to focus to solve this error ? I found some posts with related issues but none with the elements to check. Thanks in advance for your advice, Pierre-Eric