Mektul, The Forgemaster quits the fight

There is a bug where when Mektul goes into the lava to start shooting the lava waves, he instead just walks without firing the waves.
He eventually outruns the lava and keeps his slow "wave summoning" walk in the solid ground. He does not attack or do anything else and just keeps walking forward until he dies.

It happened to me 2 times out of 2 fights I had recently (It did not happen on my first character in Normal).

The last time it happened I could see him struggle to pathfind to his inteded position to start his wave attack due to my minions, so that COULD be related to the issue.