Voltas collide with elements above the staff if top staff is hidden (due to being empty)
In a score with 'Hide empty staves' being enabled and a volta and chord symbols on the top visible staff, these collide.
Woraround is to use Ctrl while adding the volta, effectivly adding it to that staff only. Downside is that the 'system' volta needs to get deleted to avoid #315248: Voltas duplicated if first instrument is invisible. or (maybe better) be made invisible to also avoid issue with (other) parts.
Seems to be happening in 3.6.2 and 3.5.2, but not in 3.3.4, might have been in 3.4 already, but I don't have that to test