One of our Dynamics 365 customers faced an issue where the "Buttons to create the products were missing in UCI App and also when opens the existing records, it shows as 'Read Only' in (Sales Hub) but works in Legacy app". In our cases, we had this issue with 'Products' entity but this can happen…
Entity Form is read only and Create buttons are missing in UCI but works in legacy web client – Dynamics 365 : Solved
Dynatecon Solutions 