In your project properties, there is an option to change the runtime to either the old Construct 2 runtime or the new Construct 3 runtime, which is still a bit unstable in my experience. I had issues with my exports while using the Construct 3 runtime and upon switching to Construct 2 runtime, it would then work normally.
So make a backup of your project and try switching to the Construct 2 Runtime option, then exporting it etc.