I had some problems with the most recent upgrade - an error required me to delete the node_modules and .quasar folders and run npm install and quasar upgrade -i again.
All good so far, but there was a compile error which I am writing about here because I am sure it will catch others out.
The error was
SassError: semicolons aren't allowed in the indented syntax.
It turns out I had to remove the semicolons around my predefined colours in the quasar.variables.sass file.
After that everything was back to normal.