Comment 3 for bug 1611264

affects me too. Lubuntu 18.04 LTS

Normally panel doesn't auto-hide, but I changed it on my thinkpad sl510. Later I tried to adjust the volume and moved mouse to panel, it showed & I clicked volume to have the slider appear, but as I move cursor up to make change it disappears when the panel disappears.

On testing, it effects network too, or anything that requires interaction with the mouse above the panel.

I can stop it from doing it via un-selecting "Minimize panel when not in use" in panel.preferences->advanced.