I had a similar issue with my THM when running dungeons. I had a xBar 1 for solo and xBar 2 for dungeons, i found when i swapped the two around the issue stopped. I don't know what caused it but it helped. As my monk I only swap bars for abilities that I don't need full time or my mount or food and stuff so its r1+O throw out buffs eat food r1+tri right after.