Hey man, been awhile since I checked up in detail. Some questions:
1) I track your log but don't watch how often you take any deloads or light days; do you have programmed light days? I know you're in LP, but you're in LP a second time, not your first, so your gross weight on the bar is more than last time, so systemic fatigue is more a thing now than your first go-around. So: Any chance your beat-up feeling is no-fooling overtraining?
2) Elbow tendonitis. The dead side-on angle doesn't show your whole grip, but your elbow height is not so high I'd be immediately alarmed. Are you proud-chesting as hard as you can? As you step away from the rack, do a deliberate mental analysis: As a percentage, what % of the barbell weight seems to rest on your back and what % in your hands? 340 is vol-PR weight for you, so maybe it's hard to assess when you're getting smashed by new weight, but it's an important metric to take. Have you taken time to pin-fire with mucho chins?
3) Knees, hips, et al. Stance width was recently a problem for me. Much more recently than it should have been for a guy who's been at this for so many months now. What's your stance width like? Maybe some video from rear or 3/4 rear next time?
4) Good-morning. Doesn't look like it in the video. I know there's a feeling where a heavy weight misgrooves forward slightly, maybe only an inch, but that inch creates a difficult moment arm to overcome due to the near-maximal weight on the bar. Your third set, the triple, here's my quick read from the sideview. Rep 1: Very, very solid. Bar speed good, depth unquestionably reached, hip drive sufficient to the task, KNEES TO LOCKED SLOT by 1/3 of descent. Rep 2 and 3: Both look like misgrooves forward, so that you have to fight them back in to get the weight up. On what I believe is a related, and likely causal note: Your knees slide forward at the bottom.
I watched several times to be sure, using background items as reference points, but rep 2 and 3, you can observe your knees move roughly 2 inches further forward when you hit the hole. I'd bet dollars to donuts that's your culprit both on the intermittent knee pain AND the balance issue. You need to find your superpower that keeps your knees from excessive forward drift.