Confirmed that this fixes issue 1, thanks!
I have made a minimal repro for you in this repo: GitHub - jthorborg/OpenGLDPIRepro: https://forum.juce.com/t/more-fun-opengl-bugs-and-woes-on-juce-8-dpi-scaling
Just press the big button.
This should reproduce issues 2 and 4 and in Ableton Live, with a minor detail change: on 2) it looks like the viewport is correct but the DPI scaling isn’t, so the OpenGL output so look significantly coarser than the standalone model. I suspect 3 might be a side-effect.
In standalone / AudioPluginHost, you should see dragging the plugin editor across to a non-scaled (or differently scaled?) display cause the weird progressively smaller resizing. In Ableton Live, it should instead crash.