@rlinnemann The most recent attempt was in that other thread but to recap in one spot with more detail, we had two scenarios. Both 2100s had the small EFI to begin with so needed a reinstall.
May 5. Client had a short power event. We found the UPS was defective, 10 seconds runtime. The router did not boot up afterwards. On the phone they said they unplugged it. I went there with a spare 2100 and a 23.01 USB install...that image was downloaded February 18 by the way, I looked now that I'm logged in. I didn't even try to troubleshoot it, I just reinstalled since I knew we had to. It booted up, I restored the config file in the web GUI, and then realized it didn't boot up after. Figured it was dead, and had about 15 minute left, so put in place the new 2100. I didn't really pay attention to the errors at the time.
June 6. A coworker went out to reinstall on a 2100 at a client's office to get it over with. He used the same USB I made since he didn't want to burn another. Installed, restored the config file in the web GUI, and it wouldn't boot, as above. Those were the logs and screen caps in the other thread. He reinstalled again, it failed the same way again, and he called me. Fortunately he could plug his laptop into the Comcast modem and downloaded 23.05 to burn on a spare USB. He installed that and it was fine after.
In hindsight we think 2) was the same issue as 1). This week the same tech used his USB stick to install 23.05 on the router from 1) above and it seems fine after a few reboots.
I still have the "bad" USB, it's on my desk at work. Not sure how the USB stick or its image could be a problem like this but it didn't get recycled yet.
When I reinstalled on my 2100 at home, a few months ago, I used 22.05 because I couldn't find an 8 GB stick at home. (edit: Etcher, btw, doesn't warn you about the space needed if you try to write the compressed image directly, it just fails x% of the way through)
Edit: I had found that other thread because there are very few search results for the "cannot open /boot/lua/loader.lua" error.