Vehicles returning to stock

Anybody know why my vehicles go back to stock form?

Known bug, unfortunately. Not sure if there’s a fix for it. Do you have more slots than you should have? Ie you should only have 3 vehicle save slots, but the bug often gives you more (for me I have 5). If you have more than you’re supposed to, it may be that only SOME of the tabs/pages won’t save, but others will.
Again, for me, I’ve found page 1,2 and 3 will not save and keep going back to the default stock form, but 4 and 5 do save.

I never looked to see how many slots I have.