Thanks for your reply! My apologies, it was an error in terminology.
What I have been doing is Group Clips.
Now, I’ve even attempted to group just the very first subclips: V1, V2 and the external audio, and I still get the same exception error. The group that it creates appears to be 15 hours long!!! I don’t know how it’s getting that. My master audio is the longest clip at 2 hours.