I tried to install fresh LE 11.0.4. After the first start and wizard completion I set an option "put display to sleep when idle" to 5 minutes. After the display turned off I lost network connection with the device.
Next, i tried nightly build LE 12 but I didn't even manage to connect to wifi because it refused my password.
That was enough for me and I went back to LE 10 where everything works fine.
I don't know why LE 11 doesn't work correctly with Orange Pi PC 2. At the same time, it works on Orange Pi PC Plus (however, with a different 2.4 GHz wifi adapter) without any visible problem.