Maintenance for the week of August 31:
• [COMPLETE] ESO Store and Account System for maintenance – September 3, 10:00AM EDT (14:00 UTC) - 12:00PM EDT (16:00 UTC)
I can also confirm this issue. It appears to be caused by one of the Mastery Skills
Thank you for that hint, I tested and believe that it's specific to the Wildfire Embers class mastery. Clip of me fumbling around while testing/demonstrating this: https://www.youtube.com/watch?v=b1ZUkSM7F8M
Edit: oh, it was also reported here, hopefully there's enough info now for ZOS to address this.