It's not a bug, just pretty terrible drop rate % after sun/moon coin game patch happened.

We didn't have sun/moon coins in the game before patch 5.0 (or 6.0) so we were dropping only ninja tools in team instances. Drop rate % of those rare tools was pretty annoying at that time and we (old players) also took a bit of time to get them, weeks for unlucky people. Currently most rewards in team instances are dominated by moon coins, drop rates of rare ninja tools weren't adjusted and it resulted in absolute cancer final drop rate for those tools.