Calendar items disappear from time to time

[Android Central Question]

Hi,
from time to time some calendar items disappear. E.g. now I saved new item. When I saved another item 5 minutes ago to the same day, my previously saved item disappeared.
It happens in every calendar app: aCalendar, Google calendar or huawei calendar, etc
I am not using sync to google account (I just save my calendar items locally on device).
Apps permissions for calendar: aCalendar, Google, Google Play Services, MyPhoneExplorer Client

Why does it happen?
Calendar items are the most important things in my phone for me.
Honor 8X, Emui 9.0.1.156 (the same happened in previous Android version, I thought it is bad internal Huawei calendar app so i installed aCalendar, for few weeks it went ok but now it happened again)