Sometimes, it happens also to me with the last SFOS 4.5.0.19 on Xperia 10 II using a VPN based on UDP with the default OpenVPN client.
I confirm that restarting network is a workaround that works, in my case.
IMHO this¹ has been closed too fast not considering all the possible cases or we are seen a regression.
¹ Android subsystem loses connectivity when switching networks