Just experienced this again. Light house using UOS built-in macro for lightning plus having cu sidhe attack.
I had a second client open at the time that was not disrupted. At this time, my character/account that experienced the issue cannot be logged in to without a client crash (unplayable). Hope we're able to find the cause to this!
If that were it, it would happen every time. Its only happneing when others are using this UO Steam macro. I've said it 50 times, UO Steam sucks and is not supported anymore. So, any packet changes could cause client issues.