Incomming calls

Guys I have a Asterisk box running trix-box ce. I installed this server back in July this makes my 12th asterisk PBX installation. The issue is The customer is telling me that when you dial and get the IVR you can press a certain ext and the call doesn’t go to the right ext. I have rebuilt my inbound rout several times. This is not a everyday problem it may happen today then come back in a few weeks. just wondering if anyone else has had this issue.