You should describe the method of "transfer" in detail. I mean button for button (change the last four digits to "9999" if there's a private phone number involved). Also post your carrier settings for all legs of the call (inbound, outbound, transfer, anything).
Not a bad idea to post CLI sample from an occurrence. Just for fun.
Note also that if you have modified "extensions.conf", you likely introduced a bug by doing so. The same applies to "custom dialplan entries" anywhere in the Vicidial Interface. Any context in extensions.conf (anywhere, even included files) must have the pre-requisite ,h, extension that harvests this data at the termination of the call and performs necessary actions (like updating dates and times, and possibly even terminating the call). Also, carrier entries must have all three required lines as an absolute minimum (the agi line, the dial line, and the hangup line).
If indeed you have a bug, an upgrade may be in order ... but I suspect it's something more like a configuration error. Just a guess though. Let us know.