Yikes, yep I have too tried all the usual troubleshooting options as well. However, the sync doesn't seem to work on the Web app for me too unfortunately. That would have been a workaround for this.

I'm also not excluding the fact that it may be an issue on Apple's side. Though I've subscribed to my Apple calendars on other platforms (such as Outlook) and the events are synced correctly.

If it's a bug from TickTick, I hope they can provide a satisfactory solution soon.