I have a 4 lock team running on the same PC and using HotKeyNet to sent keys to the four clients.
When I try to cast a channeled spell like Drain Soul only the last character in the party casts it. The others all get cancelled.

I removed all addons and even tested by disabling HKN and targeting a mob manually and clicking Drain Soul manually on each client.
As soon as I cast the spell on the next client the previous client stops casting.

Normal spells like Shadowbolt and even wanding works. It just seems to affect channeled spells.

I an running on a private 1.12.1 server of my own. I am at a loss as to what the issue could be.

Thanks for any input provided.