With this beta build installed on my RT-AC88U, I was having scanning and wireless discovery issues with my HP printer. My Plex media server also had discovery issues.
This beta some how broke the HP scan to computer feature as well as the ability for HP mobile apps [HP print services and HP All-in-one] to find printer on the network.
Plex was also affected. Couldn't find media server.
Went back to 380.64_2 and all issues resolved.
Latest Merlin beta (380.65 beta 1) has restored the ability to see the temperatures.
Also had placed a cooling pad under the router and temps currently between 71% - 73%
Having this same issue as well. Upgraded from stock Asus firmware [3.0.0.4_380_3941] to Merlin firmware [380.64].
Similar message in Administration -> Performance Tuning