Look. I get it. You guys want a clean boss fight against Liath. You want players to feel the pain of a death, and feel the pain of loss of progress. So, resetting a boss after a death seems a perfectly acceptable way to keep players engaged in a boss fight.
However, kicking the player completely out of the map, resetting discovery and mob progress, and having to redo the entire map just to get back to Liath is a bit much. At least let players continue from an empty map and engage the boss again fresh.
To be honest, this particular boss needs to be more interesting for players to stay engaged. A boss porting around in a huge room is a neat idea, but the mechanic is not very interesting. It feels gimmicky.
Add some variance to the fight. Some examples might be – Boss sometimes clones to opposite corners of the room, or large random AOE zones in the room. Something. Anything other than the current pattern…
if you want players to stay on their toes, don’t do it through punishment like map resets. Create a more engaging encounter instead. Keep up the good work. Cheers.