Rare monster disappear/fall under map - campaign

Today had the second rare monster that just vanished (and no it's not one of this annoying ghosts monssters). Unfortunately I have no proof because I'm not recording the game!

First rare monster that vanished was one of this small crawlers in Jiquanis Machinarium and second was river drake from Matlan Waterways.

All of this happened during campaign. Not only to mention that the whole campaign I barely had any loot in map or at vendors to upgrade my build.