SNMP timeout on BigIP LTM

Hi everyone, I have a problem that is making me lose my hair :).

 

SNMP on my LTM only works when I add "0.0.0.0/0" on the SNMP Client Allow List.

 

However, when I remove "0.0.0.0/0" and add the network segments of my monitoring servers, SNMP fails. The monitoring servers get no response from my LTM with a timeout.

 

Am I adding the network segments incorrectly in the Client Allow List?

 

For IP of 10.240.255.28 (let's say), I choose type "Network" and in "Address" I put 10.240.255.0 and in "Mask" 255.255.255.0. This doesn't seem to work. Any help would be appreciated...