Bugged yellow monster on Vaal Factory Map

I´ve received this bug now for the 4th or 5th time...
It is not possible to finish the Vaal Factory Map as soon as it occurs, as the mob is always a yellow one.
It also happened on another map already with the exact same mob, but I can´t remember the name of the map.

The problem is, that this mob can attack you, it will run after you and still attack you, but cannot be attacked at all. Not with aoe, not with hits/spells etc.
Even relogging doesn´t solve the issue, only dying and starting a new map and hope that this mob will not spawn. You can´t even hover your mouse over it to read a name. It´s like non-existent, but can attack you.

Can someone tell me how to post pictures of it? I tried copying the images into the text here, but it´s not possible somehow.