Ok, checked that no other devices are trying to connect to it. Even having an open browser tab wouldn't work because the browser kills those web bl connections.
After you message last month, I've given the pug a fresh battery - unsure if the old one was dead or not (didn't measure).
I went to bed after reading your last reply, the puck was "dead". In the middle of the night it started flashing red again, then stopped. It's doing that now every few hours, so the battery is not dead.
Just tried hard-resetting it again few moments ago -- puck is dead again, not responding to more resets, not advertising, nothing. I've also inspected the reported battery levels right after changing the battery on June 10th (see attachment). Started fluctuating 2h after replacing the battery, went down to 80% and stayed there until it stopped advertising and began to blink red.
I'll buy new set of batteries tomorrow, from a different place (to have a chance of different batch). Maybe the current ones are super dodgy, although it wouldn't explain the second puck which is happy with its cell :