Yup, that’s a clear sign of worn chainrings. Usually, these problems start or “become worse” after you have replaced the chain. The old, worn chain fits better into the more elongated grooves between teeth in your chainring. Your new chain doesn’t settle all the way down and then starts slipping when you apply a lot of torque.
I’d get new chainrings. Also check your cassette for wear.
For all you “front chainring knowledgeable folks,” does dropping a chain on downhills when you’re nearly spun out indicate a worn chain or chainring? Also, only happens when it’s wet/sloppy out.
This happened once on a previous wet gravel race and then again 3 times in a wet gravel race last weekend. It seems if I coast it’s no issue, but if I try to pedal lightly it increases the likelihood of coming off, usually towards the pedal.
I would have to see how the chain sits on the large chain ring. I judge it by how much contact the chain roller(s) have with the space between the teeth. Just “eye-balling,” it does look worn.
Keep in mind, new parts don’t always like old parts. Your best results may come from changing BOTH the chain and the chainring.
So it’s dropping with forward pedal action under load, or some other scenario?
Do you have a single (narrow-wide) front ring or a double? Does your rear derailleur have a clutch? If so, is it engaged?
In my experience, a new chain on worn chainrings skips when I apply a lot of torque to the cranks.
With the great length of chain engaged on a big ring (50t+, especially if in the mid to smaller cogs), it would likely take massive chainring tooth wear to lead to skipping. Color me skeptical of that as a cause (without instantly visible tooth wear) vs issues like derailleur setup, slip at the cassette (since there is far less chain/teeth engagement), non-factory brand rings (like we saw recently here) or other factor(s).
The times I’ve had a chain drop on “good” gear in the big ring at high speeds were a result of freewheel drag and or chain bounce in stutter, stall or backpedal situations. Never dropped a chain under hard load (big sprints) while the lower load & high speed drops have happened more than ones. This is with a road bike and regular derailleur (no clutch).
To add to that, my experience of worn chainrings came from mountain bikes. I have never had to replace chainrings on my road bikes.
Also, the chainring wear was neither obvious to me nor the LBS I used to use back then. That was super annoying as it happened twice that I had a spiffy new drivetrain, new chain and cassette, only to return to the shop after a few tens of meters to ask the owner to order new chainrings. So at least in my experience, chainring wear need not be visible.
Well, MTB (especially modern stuff with 28-32t rings) is a different kettle of fish to the road (and gravel?) issues above. Single ring use on aluminum material (most cases) along with extreme chain angles is a recipe for drop issues when wear is present.
Most of my experience is with MTB triple chainrings (42/32/24, I think), although it did happen, too, when I got my current 1x hardtail used. (Triple chainrings suck when you need to replace them, €€€.)
But I agree with your point that chainrings with larger tooth counts last significantly longer (i. e. road chainrings as opposed to mountain bike chainrings). Even at the same tooth count road chainrings seem to last longer (my largest chainring on my 3x XT groupset had 42 teeth, same as my Force AXS eTap 1x chainring).
Sure, but that old 3x MTB setup was flawed through the entirety of it’s existence. The greater wears aspects of dirty conditions and much more difficult use over all in MTB sets it in a different category than road setups IMO. All the issues you mention for MTB are reasons that 1x is king coupled with clutches and narrow-wide rings. Those have their own issues, but mostly different than the stuff in the OP and what I am guessing is the issue with MI-XC. Apples/Oranges
Very light load, in virtually spun out and easy pedaling just to keep the legs moving.
Single narrow wide AXS Red explorer
Was all brand new together
I wonder if it is sort of that chain speed & slack issue. That RD seems to have the Orbit tech in it that is sort of a “light” version of a clutch. In theory that should help with chain retention. But considering that this is happening in a 1x setup, on a 10t with the requisite wide chain angle, I could see it dumping with minimal load and even a slight bobble in cadence and/or road bumps.
It shouldn’t happen with the modern stuff, but component wear and the use case may lead to it. I’ve had a dumb chain drop on my MTB from simply dropping the bike to the ground off the hitch rack (rear wheel drop first with front on rack), so strange stuff can still happen even with this retention tech in place.
I’m sure all the wet sand didn’t help things. Well, all new drivetrain on order, so hopefully that fixes it.
I put on a new cassette last week and today I finally got around to going to the steepest climb around here and unfortunately the chain still slipped 
Sounds like either a setup issue or a worn chainring - presumably the small ring, which is unusual for most people to wear out first. Maybe you’ve already swapped the big ring though…
It’s the big ring which is slipping under high torque
Ah in that case that’s normal, especially if you’ve let the chain go a bit far. It often ends in a big crash so at least that didn’t happen to you!