See attached screencap for exact placement, my thistle [right] could not attack the enemies [left]. No enchantments were in play on either and in case it matters somehow, the enemy thistle had just attacked my mason. Not sure if the client considered him over water and un-attackable, but even after the mason was killed I couldn't attack so it wasn't an issue of being too far away.

Yeah, I'm already working on it for a long time

I've noticed it a few times but never thought to take a screencap as "proof" before so assumed I wasn't counting movement right or some odd thing.

Such thing always happens when one or two hexes between figures near wanted target occupied.

I finally fixed it!
Fixed in next patch.