I've been on Plusnet mobile for 2 months and everything has been great but since doing the iOS15 on all my devices at home my Iphone 11 on Plusnet comes up with the "Cannot connect to App Store... retry" message. Everything else works and the apps store on my work 8 Plus (O2) and wifes iPhone XS (3) and even my iPad Pro (non-GSM).
I've done all the options shown by Apple and others. I don't fancy doing a reset on the phone and appears strange when the other 3 devices have updated fine.
Even my Apple Watch and Macbook updated correctly. It's only this phone and only affecting the app store.