If the block that created a UI on the player screen (for example, the stock ticker in the Create Mod), and the replay begins in an area that does -not-feature this block but is later interacted with, the replay will fail to open, with a nullpointerexception.

Honestly just the ability to never have the user UI appear in the replay would be great, as it makes editing annoying.

EDIT: For example, I placed a a stock ticker and blaze burner (stock keeper) from the Create Mod down (both feature UI), teleported far away and then started the replay, when I came back and interacted with the stock keeper and then ended the replay, the replay would error with this when trying to open it:

EDIT2: It does seem that if I have replay always recording, this issue doesnt seem to occur