Hi,
I noticed the same whenever the WIFI service is restarted (whatever the reason) on my RT-AX86U since 3004.388.4 release (did not happen before).
Stopping & restarting the vpn client will show back correct info ...
Rgds,
GS
PS: there is an incoherence in your message wrt client # (gui says 3 while nvram says 4)