Some further information for posterity...
Some Logic instruments (like Sampler) support MIDI Mono Mode, which allows them to process notes arriving on different channels with different pitch bend, aftertouch, modulation wheel, and controller assignment messages. It is most useful for MPE (MIDI Polyphonic Expression) instruments (such as a MIDI guitar that can emit different notes and pitch bend information for each string).
This feature can produce surprising pitch bend (and other controller) behaviors if it is enabled for an instrument (which seems to be the default) and MIDI notes are received from a channel other than channel 1. In this situation it may appear as if the instrument is ignoring its normal Pitch Bend Range setting; and indeed it is. For notes received on channels other than 1 it uses an alternate range for pitch bend, by default 48 semi-tones.
MIDI messages may be recorded with non-channel 1 assignments if they were imported from an external source such as a multi-channel MIDI file (which occured in my scenario).
As noted above the solution is to either turn of MIDI Mono Mode from its well-hidden location (easiest) or edit all notes so they are on channel 1.
More info:
https://support.apple.com/guide/logicpro/quick-sampler-extended-parameters-lgcp3df3cd4a/mac
https://support.apple.com/en-us/HT203776