Those four tags are album gain, album peak, track gain, and track peak. As I said, only tracks with complete tags are unticked when sent to volume analysis. If most of your tracks are ticked again, probably they don't have album gain tags. In other words, your collection may contain lots of singles.
How to verify:
- Add album gain and track gain column to the main panel (they are available from "other fields" when right click on column header).
- Sort all tracks by album gain.
- Select tracks with no album gain tag and send them to volume analysis. All of them will get ticked.
- Do the same thing with complete tags. None of them will get ticked.
There's no point in keep sending them to volume analysis, if they're already done.