I use Chrome, is there any config I should know about?
You need to wait for the "ready to use offline" notification to appear.
EDIT: After completely clearing my cache, both the browser and the "app" are working normally again.
I just realized that I was always able to open the editor on the browser offline, but that I cannot through the "app" (icon on my desktop).
When I open through the browser and then proceed to "Open in Construct 3" all is fine though.
Could I've missed something? I'm using beta versions and maybe the download got "stuck" in some version?
Develop games in your browser. Powerful, performant & highly capable.
I don't know, I can only rely on my telepathic debugging skills in situations like this, and I would speculate that you had not waited for the "ready to use offline" notification while online and closed the editor before it finished saving for use offline.