It does seem not to be working, and like you I can’t at first see any reason why not.
Both your red piece, and the two white cylinders, report as Solid Group and Solid Components respectively.
I select one of the white pieces, use Solid Tools Subtract, select the red group and get only a few stray lines outside the red group, highlighted in the image below.
And this makes the red piece non-solid, so I can’t do it again with the other white piece.
The plugin Trim Keep does the same - leaves fragmentary lines and no cutout.
Certainly not what I expected!
Then I see the problem - your pieces are too small. The cylinders are only 3mm diameter, with too many edges (the default 24) for the size of the cylinder.
Try scaling up by a factor of 10, 100, or 1000 and try again. SU can’t make small edges or faces during the Subtract process.
[LATER] That doesn’t work either.
Perhaps it IS a bug? I can’t see now why it won’t work.