I've been monitoring mainly reddit for any bug or issue reports.
I have not seen any gather threads regarding any fresh damage mitigation issues. In fact, you mentioning it here is the first time I've heard of it.
Nonetheless, I have also asked the team to look into it and they have not yet found anything to corroborate your belief that there is a damage mitigation issue. They also reviewed the clip you shared. More on that below.
Similarly, our analytics do not indicate an increase in "Mean Deaths Per Hour Per Date" or a drop in "Median Lifetime by Date", both of which would have shifted if players had suddenly become squishier or started dying more often than before.
I generally try to acknowledge clear and obvious bugs and will also be more likely to do so when a large number of people confirm the same experience.
However, if I acknowledged every single time someone thought something was broken or had changed, I would end up needing to research and address the pretty much weekly topic of people claiming "Legendary Drops have been stealth nerfed" (which ALL ALWAYS get immediately disproven by other players).
Looking at the video you shared in another comment, you are fighting in the open against 8+ riflemen at CT15.
At the first damage spike you have a Breacher + 4 Rifleman in front and a wave behind. At the second spike you are in the open with all Rifleman having a line of sight to you. You can see a pause in your health drop when they finish their burst / reload. This doesn't mean there is no bug, but there are plenty of sources of damage in your video that can cause you to drop that fast.
Also bear in mind that your max shield is equivalent to your max health. In your video, your max health drops at almost the same rate that your shields do (accounting for the Tricksters innate 5% reduction bonus).
If there is a problem, the video you linked to is not the best illustration thereof. A before NH/after NH comparison may be more helpful.
If you are able to show a clearly broken functionality and other players are able confirm the same experience, I would be happy to have the team replicate that behaviour, confirm whether there is an issue and "acknowledge" it. But please do not expect me to scramble the entire team to track a nebulous issue every time a single player has a gut feeling that "something" is wrong.