Installed new chain started skipping in high gears, then replaced cluster and chainring but issue continued

I have a 2019 Santa Cruz Chameleon that has the 1×12 SRAM GX Eagle drivetrain it came with. It's had no real drivetrain issues and was shifting fine. I would occasionally tune it with the barrel adjusters early on with the cable stretch but it's been pretty good since then.

A few weeks ago I broke the chain so I replaced it with the same 12 speed GX chain it came with. When I rode it with the new chain for the first time I had some sort of skipping in the high gears (10-12) when under moderate power [was OK with low power, but who pedals with low power in 10-12? 🙂 ].

Here's a video of the skipping as it stands now after also doing all the below… https://youtu.be/FBRYoSAQvPg . It skips once right at the start of the video and once again right at the end. To simulate some power/chain tension I'm applying some brake torque. It does not skip if there is not some moderate power applied/chain tension in the system => spinning with no load does not produce the problem.

After changing the chain I then tried:

1. New cluster, like for like GX to the original – seemed to resolve the issue in 10 and reduce it in 11 and 12 but it's till there.
2. New chainring, like for like GX to the original – had no effect
3. Cleaned factory wax off the chain and lubed with Muc-off ceramic – I probably should have done this first, but it had no effect anyway

The high limit derailleur alignment seems to be just outside 12 so, from the SRAM video I watched, that seems to be right although I am not great eyeballing these things. I have not checked the hanger alignment but it was shifting fine before and I broke the chain on a climb so I don't think I did anything to it since before the chain broke when it was shifting fine. I did not touch the B-limit screw but everything was like but I did have a mechanic tune it all up at the start of last season so not sure if he may have tweaked that to match a worn drivetrain.

Next stop is a real mechanic, but wanted to see if anyone had any ideas before I do that. My wife is bugging me to get out and ride with her and I'd rather not have it sitting in the queue at a shop for a week or two if I can fix it myself. I'm sure there's something simple I should have done when changing the chain. So… what else can I try? TIA