Looking at the log you provided, this never shows you successfully making a connection.
A communication is started between the client and the server but before a full connection is successfully made the client starts another connection communication which means that the server then drops any previous active sessions. In the log you showed that cycle occurs 4 times.
Edited what I previously wrote as it was not correct.
The server makes a connection with the client which is the following line.
Normally after that there would be the udp packets being sent by the client through the tunnel.
In your case 48 seconds after the above connection has been made the client sends out another Initial packet
and the whole checking of the certificates starts again.
This Initial packet being sent by the client occurs 5 times in the above log and only once was a successful connection made. The rest of the time the client is sending an initial packet before the connection has been successfully made.
I think you need to look through the logs on the clients to see why they are starting the connection request up either during the making of the connection or after a connection has been successfully made.
If you know when a user started to get “stuck” you can look in the client logs around that time period.