R8000P dropping wifi connection

One question is are is the 5 wireless set to auto for channel selection?  DFS could be your issue as it will cause the router to drop wireless connection on the 5GHZ. 

Dropping of wireless on 5GHZ.
Problem can come up if the router is set to auto channel select which is default. What can happen is the router has selected a DFS (Dynamic Frequency Selection) channel. If the router is on one of these channels and it detects what it thinks is radar, which can be things like a microwave oven, the router will shutdown the wireless for a period of time. You can see that depending on channel the router will shutdown the wireless for 1 or 10 minutes by regulations. It is possible that due to firmware issues it may not restart the wireless.

If operating on channel 52,56,60,64,100,104,108,112,132,136,140, 5GHZ devices should detect radar signals for about 1 minute, and it should take for about 10 minutes when operating on channel 116,120,124,128 according to ITU-T Radio Regulations. Wireless client are not able to find the wireless signal broadcasting by the AP during this period.
Although DFS give you the choice to use DFS channels but it may be annoying when there is radar operating nearby. To mitigate the effect of DFS you may choose a fixed non-DFS channel if available.

My suggestion is that a channel should always be configured and pick on outside of the DFS channels listed above. I typically use 149 or 36 and do not have issues of loosing wireless channels.