I sent a DM and Glide support got back to me already 
If I understood correctly, the issue’s caused when you add the app to your home screen while it has a dark theme and then switch the theme to light.
But even when I deleted the app from my home screen and added it again with a light theme selected for the app, the bar was still visible. I had to switch off dark mode on my phone too. If I switch dark mode back on, on my phone then the bar reappears.
The team told me that they have to switch the theme to dark if dark mode’s activated on the phone. The issue is that, that change is only applied to the header.