People would still complain about them on forums, often ones run by the company who makes the client! I'm often reading threads of issues on Apple's public support forums. Being open or closed source has nothing to do with hearing about problems.
Closed software doesn't have open bug trackers, so there's no systematic way to find out.
An acquaintance of mine were twice hit with a bug that corrupted Word documents stored on iCloud if editing on her iPad. Searching online yielded others with the same problem from more than one year ago...
I was able to find complaints fairly easily. I had them listed but HN ate my comment. Search "Missing emails" instead of "delete all emails" as the latter tends to provide instructions about how to bulk delete.
> Being open or closed source has nothing to do with hearing about problems.
Also, pay attention to observation bias and userbase bias.
If my dad faced this issue, he'd never post online. He'd call me or go to a computer repair shop. That's what your average user will do.
Open Source users tend to be a bit more tech savvy. There's that famous article about Linux gamers reporting way more bugs than average users and how it can be accidentally misinterpreted as "why develop for linux?" These frequency biases are a big part of this. Pluus, OSS tends to do better bug tracking.
