Water Channel Key chest despawns on leaving area if accidentally opened

[exqz_ps]

I fought the boss that’s protecting Water Channel Key chest and accidentally opened the chest mid fight. I died to the boss before being able to pick up the key, and I left the instance to buy some food mats from Sacrament. Upon my return the chest was gone and the boss didn’t drop the key either. I can’t progress the quest because of it.