I distribute the Bitlocker-encrypted USB sticks in our company. Recently, for the first time, I had the same problem, with 2 different sticks even. I could reproduce the problem at all times on any current windows machine (Win10 20H2).
The solution was to use diskpart clean on these devices.
The possible reason for this behavior: these sticks had been used as boot sticks for portable Linux before and had just been quick formatted which somehow left things behind that Bitlocker did not like at all.