As I mention in Why does "wifi down && wifi up" restore performance?, my wifi was down and I found the STA-OPMODE-MAX-BW-CHANGED message in the logs at the point where hostapd activity stops.
Every other mention of that message that I found in the forums is related to someone having a similar problem, although I don't think they'd picked that particular message out of the logs as a possible correlation. I suspect there is connection and will keep logging things but am not sure how to add more debug, etc if it might help fix it.
In case it helps, the device that sent the message is a (half-thumb sized) TP-Link USB wifi device. See linked post above for a bit more info on its behaviour.