If the file is strike-throughs and you start the synchronize operation - the file will be overwritten.The aim of the comparison operation during synchronization is to determine which files have to be copied in which direction in order to get the folders on both sides the same.
Question mark means that with the options set it was not possible to determine the copy direction.
Such files should have "=" sign - please show us the screenshot.Files that have the same names, sizes, and dates in the right and left panes have question marks.
If you have used only name and size as compare options - then up to version 810 the files was marked qith question marks.
From version 811 it is possible to compare only by name and size (not recommended).
In red are shown files with same: name, size and date but the checksum of the files is not same.