Do you happen to have anything before that in the logs? It would be helpful to see what comes before the CTRL-EVENT-BEACON-LOSS.

Did the slate start a scan just before what you posted?

The CTRL-EVENT-DISCONNECTED reason is “disassociated due to inactivity” (reason=4), but it sounds like you were passing traffic the entire time while this happened? If you start a ping on the router to an external source, does it ever disconnect? You might try running an extended ping session and see what your overall packet loss is.