I’m also experiencing this issue and found that it happens when a client connects to an l2tp server that has multiple WAN IP’s.
Scenario:
L2TP client has two tunnels, first tunnel connects to my server dedicated l2tp WAN IP, second tunnel to general internet WAN IP.
One connects but the other doesn’t. If I make both tunnels the same IP then both connects.
Hope this helps in troubleshooting the latest version bug.
Regards