Issue with stuck DAHDI channel

I’ve setup a T1 system and running Asterisks 1.8 and using Starpy to automate it.
I can make both incoming and outgoing calls fine, however, there’s one issue that shows up once every two weeks. It seems that signaling gets into a bad state and one of the channels becomes busy forever. So if someone happens to call that channel, they get a network error. This is how the stuck channel looks like. (Channel 2)

>pri show channels

PRI                 B      Chan     Call          PRI      Channel
Span     Chan       Chan   Idle      Level        Call      Name
  1        1        Yes    Yes       Idle          No
  1        2        Yes     No      Connect        No       DAHDI/i1/1222-3456789-3

How can I find out what’s the reason for this call not clearing ? I don’t see any errors in my logs or Asterisk logs.