Fenix 5S Plus sudden increase in battery drain

My ~3yo Fenix 5S Plus suddenly started draining battery much quicker than before (100% to zero in 24h with no activity and all sensors off). I used to be able to go for a week without charging. I cannot tell what triggered the change, if anything at all. I have already tried (to no avail) all the possible factory reset procedures, including the one triggered by pressing all the 4 buttons. Now the watch is on factory settings, except that I disabled everything obvious that could drain battery (HR monitor, bluetooth, wifi, activity tracking).
The only possible remaining lead to an explanation is that in the "Debug" folder of the watch (which apparently survives factory resets), the file ERR_LOG.BAK contains an entry timestamped 7 Jan 2023 (see below) which may be exactly when the issue first appeared. This is the entry:

2900 (fenix 5S Plus) SW ver: 1800
Build Type: RELEASE
Commit:61a9197469189bb7db42684335b898ded6cd291a
ESN: 3977555971
01/07/23 22:39:37
AP
PWR RST CTRL: 0x00000082

Does anyone know how I can access someone able to read what this might mean? I'd love to know whether this may be a clue to the cause of my battery drain problem. Perhaps the watch is gone, but at least if I could tell what behavior or event triggered the problem, I can avoid it in the future. Thanks in advance!