Ok... I got your copy to work and I know why it's not working on ***your*** system!
I have Final Cut Pro 10.4.10 and Apple Motion 5.4.7. They are compatible with each other. In order for me to open your version, I had to make it compatible with my version... I'll explain below.
In your original post, you mentioned you had Final Cut 12.2 and Apple Motion 5.3. (And this threw me off...)
You actually have Motion 6.3 and it is a newer version than the Final Cut Pro version you have by one release.
You can either 1) Update Final Cut Pro to version 12.3 or 12.4 or 2) **backdate** your template to be compatible with your version of Final Cut (if you're unwilling to update 12.2 at this time.)
You can go to this Motion Template backdater and
1) Click the Browse button to locate your template (I recommend making a duplicate copy of it outside of the Motion Templates folder).
2) Set the current version of Final Cut Pro that you have installed (or in this case, just about anything older).
3) Select Upload File.
4) Click the Download File button and save it to a separate location (again).
Once you have it, you can simply drag it and drop it on the installed version in Motion Templates > Titles to replace it.
You will have to do this every time you make edits to the original in Motion because Motion will resave it with it's current version information.
If you still have your copy of Motion 6.2 (backed up), you might want to swap it out with your current version.
If you have any questions about any of this, get back with me. You can also check out this link that will explain a lot about the compatibility issue this involves.