I have a PWA that I\'ve been using perfectly till I updated my phone to 11.3 (introduce Service Workers supports, so in my iPhone it was only a bookmark) and all worked
It seems that with the last iOS version 11.4 this issue is solved, I think that now safari shares the context between the browser and the PWA and for example from PWA cookies can be accessed throw safari. But I think there's still an issue when you open the PWA and you are being redirect to login (safari opens) once you're log in you stay in the browser (iOS does not return to the PWA, but this is a first step)