this happens to me also in spa3k. intially it was just a very short ring..i don't even consider it a complete one ring.
what i did i put 35 as Ringing duration in voxalot control panel, now its up to 2 rings.
at least i have 2 rings but that's quite a long time for a ringing duration. i tried every conceivable way to solve this but to no avail.