What type and size of media? Also what valve in the TV2? I have same setup. It wonderfull!

Fine Crushed Glass. Its a TV2 with a slotted tug. sleeve. Happened with Thompson valve also

I would think either pressures wrong on pot ( blast and pot pressure not different). Or clumpy media. When is last time you have rinsed your pot out completly?
I have had some crushed glass that wasn't filtered well by manufacture and it cloged easy.

I also have the same pot and a tvll.
Maybe run it till it stops and de pressurize. Look inside to see if the media is level or if it has created a cone shape. Then it would be the clumping that Atoz talked about. Try new media.

Thanks guys. I'll try both. Media has been in shop for awhile.

If the sand is OK then it might be too much pot pressure relative to blast pressure along with incorrectly adjusted TVII valve. A big wad of media coming out when you first hit the switch usually means that the media is a build-up in the lower T fitting that continued to get pushed out through the TVII valve after the last time the main blast valve had been closed. The fact that you then don't get enough flow (after the lump is cleared out) is the TVII valve needs to be opened up. Solution is reduce pot pressure until large wad of media problem ceases then start opening TVII valve until normal desired flow appears.