What happens when network changes from mobile to WiFi

[hippo2025]

On my device (OnePlus CPH2581) network change from WiFi to mobile works normally, while network change from mobile to WiFi usually leads to VPN connection hanging for a while. What might be causing this issue? As far as I understand, when I connect to WiFi the system open new network interface with higher priority, while the old interface is still alive, so probably this is what causes the issue. But somehow other VPN clients deal better with change from mobile to WiFi