Hi,
OP here.
1) I am running RUT240 box as a simple AP mode (no hotspots).
2) When the WLAN hangs, the rest of the box seems to work ok. After once again observing the hangup, I just plugged in an ethernet cable from my laptop to the box and were able to have internet service and access the admin webui (+ log in using ssh) via ethernet. This is how I was able to look at the logs. In fact after the wlan had hung up, ifconfig still showed the WLAN as operational, while the AP did not show up in either my laptop nor my phone (I don't now enough about the RUT240 wlan hardware to check up if the driver had problems -- at least there were no relevant messages in the dmesg log). After logging in to the wlan hang up box via ethernet cable I tried the ifconfig wlan down and ifconfig wlan up and the AP showed up again.
3) No rebooting occurs, the AP just disappears (i.e. the wlan service somehow hangs)