One more comment on topic. I installed exactly the same VR600 as I use at my parents long ago and my mom suffered from strange effect - sometimes she did not received WhatsApp messages on her iPhone...

"After some considerations" ;) decided to turn my VR600 into a modem only configuration and to order a fancy ASUS WIFI6 router.

Same problem here, started to appear suddenly, Archer V600 . Latest firmware that did not changed for about a year for sure