Could you please turn your sample code here into a self-contained reprex (short for minimal reproducible example)? It will help us help you if we can be sure we're all working with/looking at the same stuff.
While you are working on a reprex, I wanted to offer a quick troubleshooting idea as I have also encountered the problem:
Make sure your "Date" variable is being read as a valid calendar date (you can check this with the function str(mark$Date)) , otherwise you will have to use as.date() to force the reading of the variables a date.
If the dates are giving you problems, check if the .csv has some format specified for date (I ended up having formatting as a date in my region of interest (English(South Africa) ) for the as.date() to work) . the number of rows of dates should equal the number of rows of animal id. I then called up the EasyMark package and ran Maker.ch function and it worked. I have just started working with the EasyMark package and In lieu of knowing more about the data, these are the only suggestions I have. Hope it can help you or someone else.