I'm referring to iMessage specifically causing tons of unnecessary problems when switching from an iPhone to an Android phone. This was over 5 years ago so I have no idea what's fixed or isn't now, but I do still occasionally have problems when an iPhone user tries to message me as part of a group.

These were all intermittent: Messages were lost or delayed for very long periods (going both ways), groups were completely broken, I couldn't tell who was messaging me because they were assigned some random source number (which I think also happened both ways), and images were compressed to illegibility.

Some people I seemingly just couldn't text with at all.

Here is just one small thread of thousands about it: https://discussions.apple.com/thread/6750172 [Not the best example, but I'm having trouble tracking down the posts I remember browsing back when I made the switch.]

It was a complete mess, experienced by many users, and it was entirely Apple's fault.