Don’t feel bad. I had the same thing happen to me–I puzzled over it a while and couldn’t uncover the cause, though, in my case, I suspect that there was something in the imported XML. My co-writer hasn’t caught the Dorico wave yet. 
Hopefully, Daniel and the team will figure out what’s happening in larger Orchestral pieces and why entry/editing seems to get gummed up. I’m sure they’ll get whatever is going awry fixed in an update.
(Most of my arrangements for piano or string orchestra don’t seem to have the problem. It’s full orchestration with 10 or more staves is where I’m seeing the issues.)