If you try to add the same Tag from your proposed alltags to your chosenTags twice right after the first one was added, you get a crash. This can happen if you fill your proposed tags from your backend.
In my case if I type "su" my backend will give me "sun" and "sunny" back. if i add the tag "sun" and keep typing "sun" i get again "sun" and "sunny", where i can add Sun again to my chosenTags.
*** Assertion failure in -[UICollectionView _endItemAnimationsWithInvalidationContext:tentativelyForReordering:animator:],
/BuildRoot/Library/Caches/com.apple.xbs/Sources/UIKit/UIKit-3600.5.2/UICollectionView.m:5585
2016-11-30 00:09:09.964160 Inline App[2760:770432] *** Terminating app due to uncaught
exception 'NSInternalInconsistencyException', reason: 'Invalid update: invalid number of items in
section 0. The number of items contained in an existing section after the update (2) must be equal to
the number of items contained in that section before the update (2), plus or minus the number of items
inserted or deleted from that section (1 inserted, 0 deleted) and plus or minus the number of items
moved into or out of that section (0 moved in, 0 moved out).'
If you try to add the same Tag from your proposed alltags to your chosenTags twice right after the first one was added, you get a crash. This can happen if you fill your proposed tags from your backend.
In my case if I type "su" my backend will give me "sun" and "sunny" back. if i add the tag "sun" and keep typing "sun" i get again "sun" and "sunny", where i can add Sun again to my chosenTags.