"Error loading attachment"?
Is your phone's memory card / built-in storage full, by any chance?
Speaking of other apps, do you use Clean Master or similar "memory optimizer" apps?
Also on Android 4.4, swiping an app "away" from the "recent apps list" -- "to clear memory" -- puts that app into a "frozen" state where it won't run in the background (until re-started by the user).
I'm curious about the "error loading attachment" message, though.
Could you capture this in the app's debug log (see my signature below)?
And to get two birds with one stone (the error and the not syncing), it would be great to first refresh "manually" to capture the error, then leave the app running as usual, to capture the "not syncing" issue.
PS - please enable "raw session data" for the log... you can send it to kmansoft / gmail