If you discover sync issues with your One Plus device please make sure you have enough free space on your phone left (at least 10%).
3-Finger-Tap not working
This is an OnePlus Issue, multitouch is not working properly. Unfortunately aCalendar cannot do anything here.
Please see also: https://community.oneplus.com/thread/730902
Notification or sync issues
OnePlus heavily optimizes the system for battery performance at the cost of app functionality, especially background services like synchronization or notifications. For guidance on OnePlus specific settings please see https://dontkillmyapp.com/oneplus