Weird, it should have been fixed in 17.02:
Does the keyboard detect the dpi at every boot/run, or does it configure itself when it is installed? If it is the latter, removing the app’s data and/or reinstalling the app might help.
Does pinch-to-zoom work with the built-in picture viewer? Seems an easy way to test whether there is a regression in the last update, as there was a zoom bug that has the same underlying cause.