After some research I found out that, the QueryTrackingBehavior of Entity Framework was QueryTrackingBehavior.NoTracking which caused problems. After turning the tracking behavior into QueryTrackingBehavior.TrackAll, all problems gone.

services.AddDbContext<AppDbContext>((sp, opt) =>
{
    opt.UseQueryTrackingBehavior(QueryTrackingBehavior.TrackAll);
//...
});