The FaxServer stops sending faxes until service restart. Over time each line stops being used until no faxes are going out. A service restart will resolve the issue temporarily. The time between service restart and needing to restart again varies between a couple of hours to a couple of days.
In the faxserver.gfi_log.txt log, you will find the warning - No Free Lines.
2015-03-05,13:06:36,179,1,"#00002200","#00004c60","info ","faxserver","SendFax() : Calling faxsrvSendFax() [124216A8]"
2015-03-05,13:06:36,179,1,"#00002200","#00004c60","warning","faxserver","faxsrvSendFax() : No Free Lines."
2015-03-05,13:08:18,311,1,"#00002200","#00004c60","info ","faxserver","Item dequeued - code  Item [1241CCE8]"
The XCAPI line monitor may also show several calls lasting long periods of time, more depending on the number of lines the customer has.
Thread guarding on the PLCI list seems to have failed and inbound calls were making it appear that lines were in use, when they were not. With lines appearing to be used for inbound calls when attempting to make an outbound call the following warning is displayed - No Free Lines.
The development has created a patch to resolve the issue. It is an update for 19.2 in the auto updates and is merged into FaxMaker 20.
The FaxServer sends faxes successfully without a service restart.