IOS vs OpenVPN - TLS error on IOS, but it works on Linux

[robnem]

Hello,

I have an openvpn server to which I can connect using Linux.
Network manager imports the configuration file without error then connects and the tunnel works perfectly.
If I import the same configuration file on IOS (iPhone 11), it doesn't connect.

I have only server side error, but it doesn't make sense (x.x.x.x is the server's IP):

Jul 2 20:51:41 ovpn-server[31582]: x.x.x.x:54341 TLS_ERROR: BIO read tls_read_plaintext error: error:14089087:SSL routines:ssl3_get_client_certificate:cert length mismatch
Jul 2 20:51:41 ovpn-server[31582]: x.x.x.x:54341 TLS Error: TLS object -> incoming plaintext read error
Jul 2 20:51:41 ovpn-server[31582]: x.x.x.x:54341 TLS Error: TLS handshake failed

The certificates should be OK.

Can somebody help me what is the cause of such error?

Thanks
Robert