(The usual "if there's a good post/faq/docs that I've missed, please point me to them first" disclaimer.)
I have a TP-Link TL-WDR4300 v1 running as a WDS master, with a TP-Link TL-WDR3600 v1 connecting as the WDS client, connected using only 5Ghz. Master also uses 2.4Ghz for regular WiFi duties, WDS client has 2.4 turned off, all clients ethernet only)
(Both running the current stable of 18.06.2, but I've had this with 16.xx and (LEDE) 17.xx as well.)
Occasionally (every 2-4 months or so perhaps), the 5 Ghz radio on the Master goes into a bad state. A power cycle usually resolves it. Disabling/Enabling the network, resetting the radio don't work. The next time this happens, what are the logs (or things in LUCI), other things to check? (I can still connect via 2.4Ghz or ethernet, ssh in, etc.)
I'm reasonably familiar w/ linux, would normally check dmesg, and /var/log/ first.