Problem with iax2 trunks dropping to only half duplex

ok, i’ve got 4 asterisk servers (freepbx distro)…

my main box is called green… i have iax2 trunks to the other 3 boxes, back and forth…

for some reason my iax2 trunks time out in one way on 2 legs

so… 6 connections…

green -> morg works great
morg -> green works great
green -> south works great
south -> green UNAVAILABLE
green -> alabama works great
alabama -> green UNAVAILABLE

each PBX is on it’s own network… after a reboot the PBX it will work for a few days it seems, then out of nowhere somebody will call and say they get a busy message when trying to call out…

so for example i can make calls from morg through green to south all day long… but if south tries to call anybody on any other PBX but their own, they get allison telling them all circuits are busy… (until i reboot and the trunk becomes available again)

if i do a iax2 debug on both boxes i can see the ACKS and PONGS and POKES going between the boxes but they don’t really mean anything to me…

was hoping to get some direction on how to troubleshoot these IAX2 trunks…

thanks,
Andrew

also, requirecalltoken is set to no on all boxes

edit2: i found out that my problems may be related to version numbers on my boxes… green and morg are older, 10.4.0 and 1.8.12.0 respectively, and south and alabama are 10.6.0… is it easiest just to back up the box and reload it?