It works fine with “rendercam.GUI_ADJUST_FIT”, thank you very much!
In the future, these parameters will very certainly help me fix my rendercam-related issues instead of posting 
Only 1 issue remains (probably nothing to do with rendercam but I mention it here just in case):
When I display the world map, the camera is supposed to automatically focus on the “current level” (when cameras are swapped). It works as intended in Defold but not with the html5 version (both mobile & desktop). Perhaps there is an error message in the background, but no console to display it, so… I don’t know.
Even if there is (probably) no link with rendercam, based on your experience do you see any generic/technical reason why the camera would behave differently in Defold & HTML5?
Anyway, I’ll run some tests, delay the initial camera positioning by 1 frame, add checks/safeguards etc.
Thanks again for the help with rendercam!
edit: just tested it again… The “camera focus” works when I build for “local” html5
but not when I create a HTML5 bundle
So weird…
Is there something specific to html5 bundles that could cause the issue? 
@britzl @Mathias_Westerdahl