It seems like circuit mode is not made for endurance game play. Playing Zephyr, I was experiencing a weird phenomenon of my warframe slowing down while the enemies are moving at normal speeds. This issue becomes apparent when I use any abilities that cause multiple damage instances. From my speculations, it could be either the decree "Fearsome Bonanza" or "Close Contagion" causing this issue. This issue does not seem to exist during normal gameplay, but shows itself only when multiple instances of damages are being dealt at very quick successions (or just extremely high volume). It seems like melee speeds will not cause this issue. (Note: These are not frame rate drops, you will be able to see the enemies moving and shooting at normal speeds, only the warframe has slowed down to an almost unplayable speed).
P.S. I dismissed the weird choppy sounds as the bullets being deflected but upon a more detailed review it seems like this might be another issue. I have never heard corrupted bullet deflection such as these.
Normal Speed: https://outplayed.tv/media/RV2K88
Bugged Speed: https://outplayed.tv/media/ywQ6y1
For DE, I do not think build matters, it is my first time experiencing this so I can only make an educated guess that frames like zephyr can most reliably reproduce this bug. This was a friends only instance but I highly doubt that matters. I will try reproducing this bug with other frames and respond back if I have time.