Thinkorswim desktop platform: 72/76 DJX call spread. Last was at 1.68 for like an hour despite huge swing up in the underlying DJX. Volume at 203. Suddenly last goes to 1.45, but volume stays at 203 ! WTF...How can this be ? A print with no volume ? Refreshed the symbol, same result volume stuck at 203.
Just answered my own question - a "duh" moment for me: only one of the sides changed, so the volume for the spread is not changed. Only spread volume is reflected. My bad.