VPN switches off when iPad screen turns off (iPad OS 18.01)

Hi,

I've got two iOS devices, an iPhone and an iPad, both of them have the latest OS version (iOS/iPad OS) 18.01 installed. Due to various reasons I use VPN on both devices which is supposed to be always on. Unfortunately, after recent update to iPad OS 18.01, VPN on my iPad switches off 2-3 minutes after the iPad screen turns off. I tried several VPNs, and all of them behave the same way - they disconnect after 2-3 minutes after the screen turns off. I noticed that sometimes I switch the screen of my iPad back on, wifi on it is off (so I deduce it works intermittently when iPad is not used, which, naturally, screws the normal VPN operability completely.) (Prior to recent updates, VPN on the iPad worked perfectly, remaining always on).

Unlike iPad, VPN on my iPhone works perfectly - on the same Wifi, with the same settings and the same VPN: it never disconnects (the only difference between the two devices, apart from the fact these are two different devices and the iOS versions are slightly different, is that, being an iPhone, it has also a cellular connection which is always on).

I would love some suggestion re causes of such a bizarre behaviour and how to restore normal VPN operation on my iPad.