HiDPI setting sometimes lost after suspend

On my Mint 19.1 x64 Cinnamon laptop, HiDPI support drops sometimes after suspend for QT applications. Normally, having the following in my `.profile` suffices to enable HiDPI scaling:

export QT_AUTO_SCREEN_SCALE_FACTOR=1 # honor screen DPI

I reported the problem to Mint but the Mint people told me to report the problem to you. As you can imagine, the problem is fairly irritating and seems to be a basic loss of functionality.

I attach the output of `qtdiag`, run when the 'reversion' (drop of scaling) had occured.

I use 'qt5 settings'. Previously my earlier efforts to get Qt working had used other lines in .profile and also the application `kvantum`.

By the way: I chose 'Core: I/O' as the component because I did not know what to put.