The marks.xml file exists in archives from yesterday and today, but not earlier. Marks.dat exists in all archives from early September onwards, all with the same early September date.   If marks.xml is removed from /Program Data/Expedition and Expedition x64 is opened there are no marks or routes in the Edit Marks screen.  If Import is clicked and Import Legacy Format is picked, and then Marks.dat picked, still nothing shows in the Edit Marks screen.  I'm guessing the data is in the old format in Marks.dat but I can't figure how to get it to read into 12.1.2.

Had the same thing with last update last week . Running v12 since release But my mark Dat file doesnt exist that contains everything since the update. Im guessing and its probably written somewhwere that the mark data file is in a new directory with different file  extension now?

i have the similar issue
updated to v12 with navionics charts from cmap and i lost all number windows and marks
i have managed to make new number windows but i cannot get the marks back
i have re-imported marks many times, if i re-import my old mark database it causes expedition to crash and close
if i clean up my mark database and re-import it then the marks appear
however when i close expedition and open again there will be no marks
this is the same for when if i try to make new marks from an empty mark database
as a workaround i have had to export marks to gpx and import the gpx file every time i start expedition
had to do this a couple of times during a race yesterday

Thanks, will look at that.