SIP part hangs (Asterisk 1.8)

Hello,

Having an issue where SIP part of Asterisk is hanging up.
I suspect that chan_sip.so module hangs up completely, because:
SIP calls are not accepted at all (no traces on Asterisk of these calls).

New IAX calls are entering Asterisk and looking good, but hangs on part where it should be terminated by SIP device:

Dial(SIP/xxxxxxxxx@xxxxxxx,60,L(14397000:60000:60000)iIgM(agi_script,1445255469.55011))
[Oct 19 13:51:09] VERBOSE[2710] features.c: > Limit Data for this call:
[Oct 19 13:51:09] VERBOSE[2710] features.c: > timelimit = 14397000 ms (14397.000 s)
[Oct 19 13:51:09] VERBOSE[2710] features.c: > play_warning = 60000 ms (60.000 s)
[Oct 19 13:51:09] VERBOSE[2710] features.c: > play_to_caller = yes
[Oct 19 13:51:09] VERBOSE[2710] features.c: > play_to_callee = no
[Oct 19 13:51:09] VERBOSE[2710] features.c: > warning_freq = 60000 ms (60.000 s)
[Oct 19 13:51:09] VERBOSE[2710] features.c: > start_sound =
[Oct 19 13:51:09] VERBOSE[2710] features.c: > warning_sound = timeleft
[Oct 19 13:51:09] VERBOSE[2710] features.c: > end_sound =
[Oct 19 13:51:09] VERBOSE[2710] netsock2.c: == Using SIP RTP CoS mark 5
nothing is happening after this.

while next entry suppose to be:
– Called SIP/xxxxxxxxx@xxxxxxx…

What could be the reason of that
or where should I look to trace down this issue?
Thank you.