I work in the film industry side of lighting and we use HMI’s all the time (sometimes without the UV protective glass if the gaffer is a cowboy…). I’ve never really run into this with theatrical/event lights when we do use them…but then again you seem to know about situations like this.
There are so many old gaffers who have cataracts now because of all of those years looking directly into the hot spot of a carbon arc.
You’re probably correctly blaming the board while I think it was Aliexpress lights with actual UV emitters.