Printer will not connect to WIFI all of sudden, creates RatOS hotspot instead

For context, the printer has been working for about a year with no problems. I've had similar problems with one RPi 4B+, swapped for new one, it was fine for two weeks and now the same again.
Router was set to DualBand 2.4/5 GHz initially, I tried splitting to 2.4 and 5 GHz separate networks, no luck.

Resetting Router helped just now.
But I'd like to avoid this stuff in the future. Are there any troubleshooting tips?
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