Issue with syncing using iCal, Acuity and AddEvent

I run my own business and use iCal, Acuity so clients can schedule and pay for appointments on my calendar, and AddEvent (calendar feeds for my paid community events).

Up until a couple of weeks ago, these 3 systems got a long nicely. All of a sudden, Acuity was double booking me over my AddEvent events. The AddEvent subscription feed was not being pulled into Acuity any longer, despite everything being set up correctly.

I have talked with Acuity and AddEvent, and they have said it is an issue with iCal.

But no one knows how to fix it.

So, here I am, wondering what the heck did Apple change that is causing these systems to not communicate anymore.

I can't keep getting double booked and rescheduling clients. It's very unprofessional and a frustrating experience for clients.

My only fix is to do double the work and update 15+ events on AddEvent so my members have these events saved to their personal calendars and then manually duplicate those events on my personal iCal so Acuity will read them.

Any ideas on how to fix so I can get the automations working again???