Were you generating a MIDI solo or a RealTracks solo? You can tell by looking at the colour of the track in the mixer - green is RealTrack and yellow is MIDI.
RealTrack solos can't be edited by editing the MIDI, except if you're using a 2022 or newer version of BIAB. In those versions, RealTracks can be edited by using the Playable RealTracks functions: