In nexus blitz, I fought a Jhin who would shoot all 4 ult shots at once. I initially thought it was tied to activating Sword of the Divine, and tested it myself. However, I was able to recreate the bug with or without the item in my inventory and was able to spam the R button and shoot all of the shots. Hope this helps! I also have not tested it on normal Summoners Rift so I'm not sure if it's just tied to Nexus Blitz or not.