Could be a SDV capacity issue or signal issue or even a code malfunction in Navigator. iGuide has a bug where you lose SDV server connectivity and sometimes have to reboot the box to get it going again. I know various areas use different number of SDV QAMs the most I have seen used in any division is 24 which the North Texas (Dallas metro) system has set aside for SDV. When SDV was first deployed we had 8 SDV QAMs during the launch period where they were only switching 24 HD channels to get the system running and then it went to 11 SDV QAMs while the system was having the QAMs rearranged to make room for 16 total SDV QAMs and then on the final push another group of HD 3:1 QAMs were moved to SDV and then we went to 16 SDV QAMs and they started adding more channels at first none of the SD digital channels were moved over to SDV and for a while the only SD SDV channels we had were new adds and then in 2011 TWC did another reconfiguration where they moved a ton of SD channels to SDV and freed up 12 or QAMs for SDV and eventually VOD got another 4 QAMs out of this change as well
so the North Texas TWC system is loaded:
24 SDV QAMs
8 VOD QAMs
6 DOCSIS downstreams
thanks to a 860MHz rebuild that was done from 2006-2008
so the North Texas TWC system is loaded: