Back in April we first released an alpha of a brand-new runtime for Construct. This has been completely rewritten from the ground up and brings huge performance...
Have you tried Safari 12? There are bugs in Safari 11 that prevent it being able to load the C3 runtime.
Just double checked and yeah I'm running 'Version 12.0 (14606.1.36.1.9)' I appreciate the construct 3 runtime is still In beta.
Please file a bug following all the guidelines then.
Ok done. Looking forward to using the new runtime though :)