My timezone is PDT, and seems like calendar somehow got hard coded at GMT +0:00 or something similar, everyday after 5pm it defaults to the next day.
You can observe it from screenshots, where calendar is on incorrect date (next day), Snapshots view got the date right, also attached iOS calendar for reference.
I've checked my iPhone, Garmin Connect account, Fenix 3 and they all have timezone set to PDT correctly.
App version 3.17.0.10