Yes, that is almost certainly the problem. The intention is for Dorico to act as if the divisi had never been created once you delete the final divisi change signpost, but there are a couple of bugs in the current version. This will be tightened up in the forthcoming update. For the time being you can create a new section player holding the appropriate instrument and copy and paste the music from the old player to the new one, then delete the old player.