Harvest Boss stuck in wall and unkillable

I was doing the final map in a harvest memory from Einhar and got a Harvest Boss spawn. The boss got stuck in a wall and is now unkillable (bottom left in the image). The boss can still use all their skills but can't move from that spot, even when using the skill where it sort of teleports and it can still be attacked but it wont get damage anymore.

I managed to get it out of that spot by spamming frost wall for a couple of minutes. But he is still unkillable.

Having same issue, and its quite common, not only stuck in walls, but just generaly refusing to phase, continueing its attacks for ever even at the phasing threshold.
this happens to me in like 1/15 or 20 bosses i find. and since i farm harvest memories, this occurs multiple times a day. have not found a fix yet, generaly it just bricks my harvest.
it seems it gets stuck at the same spot, the lower right corner. prob would be a good idea, to leave the plot last and try to not stand close to there so they jump charge/jump there aswell.

Just happened to me in the exact location.
Knockback support wouldn't budge him or even ice walls.
Void sphere did not do anything either.

Regular monsters get stuck there aswell, but since they dont have immunity to damage they can be killed, but they also cannot leave that spot. should look into the terrain there.