Pushing from macOS Calendar to Server: Sometimes immediately, sometimes delayed (with next sync interval)

[porg]

The good scenario

• Idle for long time.
• Create a new event.
• etesync-dav immediately sends to api.etesync.com
• In other words: macOS calendar and/or etesync-dav seem to not "queue" anything, but macOS calendar seems to immediately contacts etesync-dav running on localhost, which immediately contacts api.etesync.com (monitored with https://www.obdev.at/products/littlesnitch/)

The bad scenario

• Do not know what exactly the precondition is. Active in macOS calendar? Active for a while overall?
• Create a new event.
• etesync-dav shows no immediate a internet network activity!
• Investigations & Assumptions:
• macOS Calendar.app > Preferences > Accounts > etesync CalDAV account > Refresh calendar: I have set this to the shortest possible. This seems to only affect the download interval. Uploading is always immediate. Proof: When running etesync-dav -D I always immediately see that VCALENDAR […] SUMMARY: is exactly the title as I typed it.

So why does etesync sometimes upload immediately and sometimes only many minutes later? Does it have a queuing/treshhold mechanism also to avoid server overload?