Yes, I can force the problem (just put on higher channel and reboot). Where are logread and dmesg located? It already took some effort for me to figure out how to retrieve the other file, but I don't know where this is.
There you go.
Thank you. While working on it, I also noticed that I was now able to select channel 14 (this wasn't the case a few days ago I think, no idea what changed). Which I think should not be possible.
Anyway, the files.
I'm no expert or anything, but I've read a little through it and noticed this:
Sat Nov 24 14:59:32 2018 daemon.notice hostapd: wlan1: interface state UNINITIALIZED->COUNTRY_UPDATE
Sat Nov 24 14:59:32 2018 daemon.notice hostapd: Channel 13 (primary) not allowed for AP mode
Sat Nov 24 14:59:32 2018 daemon.warn hostapd: wlan1: IEEE 802.11 Configured channel (13) not found from the channel list of current mode (1) IEEE 802.11g
Sat Nov 24 14:59:32 2018 daemon.warn hostapd: wlan1: IEEE 802.11 Hardware does not support configured channel
That's odd, as CH13 works fine in original firmware and it's also working if it has been started correctly once (I verified with WiFi Analyzer that it does indeed set it to CH13). When I tried OpenWRT (didn't like the complexity of it) I had no problems setting it to CH13 either.