Unkillable rare mob (bug report 2.321.793.740)

I have an unkillable, untargetable rare mob in a t15 Vaal Factory. No life bar, doesn't show anything when i hover over it.

It seems to be stuck halfway in the ground

I have a similar issue with the same type of mob in a Tier 5 Vaal Factory
Bug Report Reference Number is 3,612,864,201

I think it was a duplicated rare mob in my instance of encountering it. My minions completely ignored it and various AoE skills did not appear to affect it.