I ran Algeth’ar Academy on Mythic 0 difficulty.
I killed the Vexamus, then Crawth, then Overgrown Ancient.
After that, I took a break.
I went back to the instance which was reset (as I expected).
I re-killed Vexamus and Crawth.
When I walked into Ancient’s area, but there was no trash or boss.
There were just two friendly NPCs casting red and green magic, doing their standard thing.
The way to the last boss was blocked with roots, so I couldn’t proceed forward.
The only NPCs that gave me dialogue options were the five buffing dragons from the beginning.