I’ve noticed a glitch with Oath of the Sustained, and also Enraging Artificial Vitae (and probably all other health regen gear).
I was just playing with Pendles and my health regen dropped permanently from 12.67 to 5.1
And before you say it, no I was NOT wounded was out of combat for a minute and it was still at 5.1 regen 
Were you running any minus CC gear and/or went for his level 9 -CC duration helix?
Were you using his legendary?
I don’t think that was a glitch with OotS. I was in a match about a week ago and after being wounded I was unable to regen or heal from a healing station. I was sitting there for close to a minute before teleporting back to base where it began working again. But for that minute I was at +0 hp while wearing regen gear next to a station. Which is really annoying in the middle of a key push and you have about 100 health left!
Literally only happened once (at least that I noticed) and chalked it up to a rare bug.
Was playing a Bots match as Toby last night…
Each time I passed our accelerators my shield went down.
Never saw that before.
Well the question here is can you get it to happen again. Once can just be glitch or happenstance.
Play another game, or maybe a PvE mission, and make sure you do not have anything that reduces healing received. If it happens with any consistency, then we got something to look at.