(as I recall) I have used openwrt on a RT56N, a Fritzbox 3762SL, a Netgear 3400, and a SmartRgsr400ac. Over the time I have seen some issues. I have used it in simple NAT bridges and network bridges to apple ipheth. Ultimately I am feeding though a Apple iphone hotspot the whole time.
(1) The main one that I don't really understand is when I use yt-dlp, randomly I get like 60% of the downloads, the message urlopen error -2 name or service not known. It seems on the router this does not happen (don't quote me but that seems to be the case). So today I tried using tinyproxy in a weird way, to make me look like the router when I used yt-dlp --proxy and also my browser I am now using through this proxy typing this.
(2) Even with other persons equipment I see a lot of like google searches, facebook pages that I click on and then remain totally white and finish.
(3) The Fritzbox was known to reboot itself outright when I was using an iphone tether from time to time but seemed ok using a usb storage stick.
(4) The netgear would seem to just pause on the NATed side every few hours for like 2 minutes and then continue to work normally.
All my devices had like 19.07 I think it was a few back, but the sr400ac has the newer one.