Date/Time formats using commas instead of semicolons will cause iOS compile to fail.
"LogPlayLevel: Error: ERROR: System.FormatException: Input string was not in a correct format."
Similar Unknown Char bug on AH: https://answers.unrealengine.com/questions/728244/iphone-launch-packaging-fails-with-systemformatexc.html
Also reported occurring if alternate locale is used when deploying directly from Mac.
Result: LogPlayLevel: Error: ERROR: System.FormatException: Input string was not in a correct format.
LogPlayLevel: at System.Number.ParseSingle(String value, NumberStyles options, NumberFormatInfo numfmt)
LogPlayLevel: at System.Single.Parse(String s)
There's no existing public thread on this issue, so head over to Questions & Answers just mention UE-68830 in the post.