Please do not use SelUnqUnit anymore. Revert to SelUnqSubUnit, which is better in all aspects.
A unit is a too temporary container structure since AACW to be relied upon and you should not rely on a search at this level since BOA. Searches at a SubUnit level (called element for non modding players, but SubUnit is the legacy wording, still used in commands) are more precise.
Reminder: Even if you issue a SelUnqSubUnit command (that succeed), you will get an updated selector on the subunit you seek, but also the parent unit and parent group. So you can use RemoveCuUnit if you need to...