I opened files from the schism of the Roman Catholic Churches and Eastern Orthodoxies. I was right...my brain is too tired right now to read it all.
It's way too much to absorb. I will leave it to the doctors of the various churches. They have made it their life's study and work. But I saw one vaguely remembered term, "filoque," for one, and my brain shut down from fatigue. TOMORROW!
I really don't think there are any truly theological issues as much as there are issues of authority and autonomy (who chooses the bishops) and some canon law disagreements. I don't even think the filioque is so much an objection doctrinally.
How it got add to the Creed is the issue.
These are my opinions. I'm mlost likely over-simplifying things.