I am still experiencing this problem.
Just installed the latest version of Gravit on Ubuntu 18.04.1 LTS from the software centre. I get the error pretty much everywhere that is not something in my Home folder.
But these are all locations where my user has full ownership, and I can reach with any other program.
I also tried to install Gravit from the command line, adding the --classic flag (as suggested in some previous comments) but I got the following warning in the console which did not allow doing that:
~ sudo snap install gravit-designer --classic
Warning: flag --classic ignored for strictly confined snap gravit-designer
Can you please do something about this?