After updating project from 11/16/2020 to 05/31/2021, the grid columns persistence not working correctly. I saw that all columns are saved to database (visible with order index and notvisible with index -1), but after opening the screen again, all columns are shown, nevertheless that some of them are with index -1.
unfortunately you are right: there is/was a bug in the FIXGRIDDefaultPersistence which was introduced with 20210503_2.
We fixed the bug, it is officially available with next week's update. We created some interim build in addition + provide the corresponding download information to you.