LTP5902-WHM gets prolonged "Not ready to send" alarm while in OPERATIONAL state

I am running an LTP5902-WHM in an office which has several other similar devices, all talking to an Emerson 1420 WHART gateway.  The Emerson is about 30 feet from my LTP5902.

My LTP5902 is in an OPERATIONAL state, sending data to the gateway using "Send" commands every 8 seconds.

Several times a day the LTP5902 gets a "Not ready to send" alarm while in the OPERATIONAL state.  The "Not ready to send" condition lasts for about 3 minutes, then clears by itself.  The problem has occurred in two different office settings.

"Send" commands do not send data while the alarm is present, and the "Send" command returns error code 12 (No Resources).  I can understand why I get this result code.

My question:

Is it normal to get intervals of "Not ready to send" while in the OPERATIONAL state?

Is there anything I can do to prevent these alarms from occurring?  Or is there anything I might be doing to cause these alarms?  Could this be related to other LTP5902 devices joining and unjoining on the same network ID?