my turn:
Could be ... Illegal numbers!For instance (in the USA) any 10 digit number with a 0 or 1 in the 1st or 4th position or 11 digits or 9 digits.
If you have numbers that do not fit the dial pattern for your carrier, those calls are requested (and count as auto-calls, which block more calls being generated), but they don't actually appear in the asterisk CLI, so vicidial scripts never 'attach' and manage them. This includes the cancellation of the call after dial timout seconds. So the system loses track of these calls forever leaving them in the auto-calls table, blocking any more dialing. a reboot them dumps that table and calls fire up again.
We use an "s" extension in a general/catch-all carrier to be sure this doesn't happen. Any numbers that fit no dial pattern will auto-attach to the s extension, which merely initiates vicidial (call_log entry, line 1) and then hangs up (ordinarily line three) without bothering to dial since the number is invalid.
Possible.