I think if you are looking for a proper diagnosis or help you would need to provide the typical info. I’m not an aro guy but to save Time, I’m sure the next person who comes on will ask
Water parameters
Tank mates
How long has tank been set up
Are all fish new to tank
Was it eating etc...
Ambiguous answers will often prevent you from receiving the info you are looking for.
For the record, I would also like to know what happened here, if anyone else knows what is up.