You can lock the bootloader on /e/, iode and CalyxOS (and stock FPOS of course) and all of them actually encourage you to do so, so yeah this is a real problem.
If something goes wrong when locking the bootloader and get_unlock_ability was somehow (no one has figured out how) reset to 0, the phone is bricked and can only be repaired by Fairphone.
Since this is a flag that should survive factory resets (and it survived the phone being flashed back to stock on my devices), I’d expect Fairphone to have knowledge about where it’s stored and what could be messing with it.
Even if this turns out not to be a Fairphone problem, some help for the community how to figure it out would be really appreciated. I’m pretty sure they don’t want unnecessary work for their support staff either…