looks like you may have some bad geometry in the model… those odd streaks of red look like planes in the model.
In the bottom image you can see the ghost of planes extending from each of the holes thru the transverse bar.
These are showing up as unsupported minima because those planes are discontiguous.
At least- that’s my best guess.
I would orient even taller so that you might eliminate supports on the ribbed rim of the circular end pieces.
But the red streaks should not be there if the model is a properly watertight solid. Whatever app you modeled it in- check for duplicate surfaces or co-planar polygons or surfaces that are not part of the overall model.
Here is a fixed version of the STL. While it still requires minor fixing when it’s imported into PreForm, it will no longer have the issues you see above.