Does this occur only when the traffic load increases ? If it will stay stable at low traffic load then only occurs at hight traffic loads then it could be a problem with radio congestion.
The classic sign of congestion on the radio network is Retries and Max packet retries counters and Discards are increasing These can be seen on the root radio port page
Max Retry Packets—The number of times request to send (RTS) reached the maximum retry number. Click Set Properties to display the Root Radio Hardware page, where you can set the maximum RTS value
Total Retries—The total number of retries that occurred through the radio port
If you have a high number of CRC errors that often indicates interference then this can also case congestion on the radio interface as the bridge tries to transmit but detects the interference and holds off the packet (a retry)
If you see Max retries incrementing and no or very few CRC errors then try setting the etherenet port and and the switch port to 10M half duplex ( radio port is 11M Half duplex so this means very little buffering should be needed by the bridge) and use the switch and or router to control the traffic rate via QoS
If you see these error messages with no or very little traffic then I would suspect an RF link problem
