Can't target beast corpse / when I try to use Necromancy net it says "Can only capture beasts"

I have Summon Zombie Gem equpped. That green thingy was Legendary crab I would like to capture. :/ My friend couldn't nor target / nor capture it either.

I've ran into this problem a few times. Whenever my totems kill a Craicic beast, I switch to my detonate dead and was able to target and detonate the irrelevant mobs, but I eventually I wasn't able to target any more corpses despite obviously seeing the one I was trying to capture right there under my mouse.

Same issue as over here: https://www.pathofexile.com/forum/view-thread/2111676/page/1#p15395015

All appear to potentially be the same monster type.