On several Tenants ther is a problem opening Sharepoint New/edit screens created in Power Apps. The SharePoint list Works well, but when i try to open a form, it start opening the screen and then it stop. It is not possible to get Access to the data.
@TrulsB one thing you could try is to temporarily revert to the default SharePoint form for the list (go to List settings -> Form settings). That will give you the original form. Then go back to List settings -> Form settings and change it back to the Power Apps modified form. You'll then need to go to Customize forms menu in the list, make some minor change to the form, save and publish it. Hopefully that will get your customized form back.
Rob Los Gallardos Microsoft Power Automate Community Super User