Non Pre-cached URL

[danyill]

After working for a few minutes in https://openenergytools.github.io/scl-editor/ I often see the following error in my browser debug console:

Uncaught (in promise) non-precached-url: non-precached-url :: [{"url":"/index.html"}]
at O.createHandlerBoundToURL (https://openenergytools.github.io/scl-editor/workbox-9f2c24b2.js:1:13245)
at Object.createHandlerBoundToURL (https://openenergytools.github.io/scl-editor/workbox-9f2c24b2.js:1:14600)
at https://openenergytools.github.io/scl-editor/sw.js:1:3411
at https://openenergytools.github.io/scl-editor/sw.js:1:565

I am not sure what causes this, whether it has an impact on functionality or how better to diagnose it.