I think I am using the same script, but instead of using the collection "title" use the collection ID (SMS0001 etc)  seems to work.!  but I do not try to run updates immediately, I have a Update group targeted at the unknowns, but if you have specifics... I basically assign to a maintenance window and wait to the cycle to pick up anything missing.  We update the deployments quarterly, so there are generally only a few missing.  I would enable incremental updates on the collections that you are hitting, so they see things "quickly"