At the moment we are investigating reports of SUP 2.1.3 native synced apps on iOS that crash unexpectedly.
It seems that after 50-60 consecutive syncs, the app goes ballistic.
To get rid of this behavior, forum member SUPFAN has indicated that you got to close the connection after your sync:
"add [xxxxxDB closeConnection]; after your synchronize() line"
I am not sure yet, if this is just a works as designed issue or a bug or documentation issue. Under the line, you got to make sure to keep this in mind when developing native synced iOS apps on SUP 2.1.3 (and probably higher (SUP 2.2).