The Sensel Piano overlay mode is not sending MIDI notes below 60. This only happens when using the Morph script - creating a generic keyboard input and then selecting the Morph as the source allows MIDI notes below 60 to be played. However, since it is a generic standard MIDI device, MPE is unavailable.
Currently there is no way to use the Morph’s Piano overlay with MPE in Bitwig Studio 4.0.1
I had a back and forth with the Bigwig Support team to confirm this behavior.