That is all a bit weird   However, there's a couple or three things I'd suggest:

1. Make sure you are running the latest POD HD firmware (1.43).
2. Power the POD from a stable power supply - a regulated power supply (i.e. Furman) would be the ideal answer but not cheap.
3. Re-flash the guitar's flash memory.  I'm not convinced this will actually fix it, but to rule out corrupted flash memory code, you should do it anyway.
4. Try a different VDI cable - again it may not resolve the issue, but would rule out a problem with your current cable.

There's really not a lot else that you can do without voiding your warranty on the guitar.  I'd hazard a guess that unplugging the VDI cable and re-plugging it clears the issue anyway, but if the problem persists you may have a physical hardware problem, in which case you need to take it in to your nearest authorised service centre for assessment, but with the problem being intermittent it may be harder and it might take a while to trace the issue.

If I were a betting man, I'd say that if you connect the guitar's VDI cable just before you play your set at your next gig, the guitar will work flawlessly to get you through the gig given the problem seems to only occur occasionally.  But I'm not a betting man

Nick