I have not received a Dropbox invitation. When I do I will be happy to look a the video and will also share with Lisa as she does MAC support. I am very familiar with Dropbox so that is not a problem.
I assume you realigned your laser to the registration marks when you put tried to cut the earlier copy? Did you adjust the cut file in any way between the two files. It could be that there is a difference between what you printed and what you now have showing in the software. I have done that accidentally before - it will mess you up every time.
Why don't you print a few more from the file you have now and see if they consistently work. Just use copy paper or whatever you have that is inexpensive to be sure you are getting good cuts. You would at least know that things going forward are working.