Hi, I am having problems with my MacBook disconnecting on 5ghz wifi.

I have the following,

2860AC (fttc) - Ap902 (office) connected with ethernet to the 2860AC - AP902 upstairs in AP Bridge WDS Mode (separate SSID for upstairs).

I have my Qnap Nas connected to the AP902 (office) with ethernet and my MacBook on 5ghz running a backup to it. The problem is that after a few hours it just looses the connection, if i switch to 2.4ghz it is fine. My MacBook is only 10 ft away and I have never had any problems with any other brands of AP/routers etc.