Ideally you’d isolate the UPS as the problem, so it would be good if you could borrow one for a few days or so to check. It could be that the UPS isn’t the problem.
Consider reviewing the return policy of a company where you can get a pure sine wave inverter and if it fixes the problem you’re good, and you’ve already got your replacement. Else, there may be a configuration or hardware problem.
Well, might have to do some isolation tests if you can borrow a pure sine wave UPS and see if it makes a difference. Outside of that, the power blip might be too much for the power supply to handle or it trips up BIOS/mobo voltage sampling.
There are some devices which will protest under modified sine wave, and some which may even get damaged. I recently accepted the risk of using an msw inverter with some electronics and did not notice any issues, but I had read that the device would be fine with it.
Would a chip-scale atomic clock (CSAC) do what you need?
This is promotion for a conspiracy theory site dressed up as a TIL.
That’s my thought, that the power blip is basically too long, and why I suggest to OP to try a different UPS.