I wrote this as a comment to another question, but I guess the situation was a little different, and the solution did not work for me. https://www.mathworks.com/matlabcentral/answers/331053-appdesigner-project-not-opening
I have an app that I wrote in 2016b. I have since modified it in 2017a. I have tried copying the file to different computers with different versions of Matlab. The file seems to run correctly in 2017b, but it won't open. I only get a dialog box saying 'Error loading XXXXX.mlapp' but no other information. This was tested on two distinct computers. The file opens and runs correctly on other computers with 2017a. The Matlab licenses were not the same between the computers if this makes a difference.