Item | Split (and
Item | Join) does use the separator text configured at
Tools | Options | Import | Separator text for appending/joining/combining/splitting. If you want to split on new lines, enter one or two blank lines as the separator.
https://kinook.com/UltraRecall/Manua...portdialog.htm
When splitting, the item title is always based on the first line of text in the new item (truncated to
MaxCharsForItemTitle at
https://www.kinook.com/Forum/showthread.php?t=5097).
See
IncludeItemTitleOnJoin at
https://www.kinook.com/Forum/showthread.php?t=5097 for configuring whether to include the item title when joining.
You might try restarting UR or compacting & repairing your database if you're getting an error message like that.