I am a new Instinct 2S owner using an iPhone with iOS 18.4. I found that calendar entries from my iPhone only sync to my Instinct 2S after rebooting my phone. Any subsequent changes to any calendar entries will not sync to the watch until I reboot my phone again. This happens every time.
Rebooting the watch or changing the Connect app calendar permissions, disabling/enabling bluetooth all do not help. The only thing that brings the calendar to life again is a reboot of my phone.
All other smartphone features (notifications and weather) work just fine as they should, only the calendar sync has this mentioned issue.