This is an undocumented change that is a consequence of the new nametag implementation.
Using certain characters on the old system would appear as empty spaces in VRC, allowing people to use otherwise taken names (for example IIRC Merlin, the creator of U#).
Although Tupper said this is an intended change on the Open Beta Discord discussion board, this is worth bugging anyway to both provide visibility here and record specific feedback on this undocumented change.
My view: the problem appears to stem from the link between username and the UID that VRC uses to identify people. Whilst it's probably far too much work to fix this after so many years of development, at the minimum refreshing the name change timer on release would allow people to mitigate the change.
However, I'd encourage VRC to consider releasing long-dead VRC usernames back into availability. This is good practice which has been adopted by other games with this problem over the years.