First thing, even if it surely won't solve anything, is to try to autilize another browser where you definitely don't have caches or similar things saved, and test if the same error occurs.
Next, since you said you don't know if this occurred after the C3 update, I suggest you try to downgrade the Construct version, and check if the error occurs anyway.
Finally, if you still can't fix it, try creating a new project, and copying the various project settings into your project (before doing this make a backup copy of your project so you can recover all your settings in case the problem doesn't resolve).
Unfortunately, since we don't get a specific error from the export log, we have to proceed by trial and error...