Having just spent a few months reading circadian entrainment papers for a circadian rhythm app I just finished,[1] I wonder if this effect might be about circadian amplitude[2] (rather than phase, which has gotten more attention).

[1] https://www.impulsearc.com/wavelength/

[2] e.g. https://www.nature.com/articles/s41540-023-00300-w

Also just the general timezone stuff, genetics ~ I've moved from the right end of a timezone to the left end, it's been killing me.