There are, imo, different steps involved in learning to read notation. First comes understanding the actual notation for pitch and rhythm. The other step is being able to read music at tempo. I guess the last step is being able to sightread at tempo…this takes years to master. The other complication include key signatures, choosing where to play a passage on the neck as you are reading it, and, in the case of a lot of written out jazz parts, dealing with rhythms that are not exactly as written and parts produced by non-bass players that are unplayable as written. Then, at last you master all of this, get a pit gig for a musical, and have a singer need to go down a step on the night….
please don’t get discouraged though…all it takes is time