External Paging connected to a MM711 port

[zildjain15]

I have 4 G700 gateways (different sites connected back to an S8700 server) with external paging systems connected to an analog port on the MM711 module. This is setup through a trunk group and accessed using the TAC for that trunk group. Most of the time this works fine but on occassion I have to busy and release the trunk group or port because the trunk group doesn't release the port as it should. It doesnt' happen everytime. I first thought it was user error due to someone not hanging up the phone after they've paged but that only explains a few cases.
I been told that the modules may need a HW or FW upgrade but the last site that reported this has the latest HW/FW on their MM711 modules.
Has anyone else experienced this or know of a poosible fix?
Thanks