Tube Screamers can be tricky on bass.Every TS variation I have tried doesn't work well for me, but I have a friend that has like three of some TS variant on his board as he biamps and his sound insane. I could never get it to work for bass.
The signature Mid hump in the TS EQ curve at around 720hz, and bass and treble cute associated with it, isn't always awesome on bass depending on other EQ stages.
Usually takes some adjustment in the Mid center freq, some other creative eq-ing elsewhere (Amp, other pedals, stacking other drives), or a clean blend of some kind.
This is likley why stacking the combo of a Big Muff and Tube Screamer on bass can be a big help. It brings back some of the mids the Muff circuit naturally cuts.
