To reproduce: create a strippet browser in pbi (I'm using the dev visual to do so). Bind at least Document Id and Title Image. Switch to outlines mode. Switch back to Thumbnails mode. The following appears in the debug console:
Warning: a promise was created in a handler at webpack:///./src/StrippetsVisual.ts?:1096:43 but was not returned from it, see http://goo.gl/rRqMUw
at new Promise (webpack:///./~/bluebird/js/browser/bluebird.js?:2805:14)
at Thumbnail._loadImage (webpack:///./lib/@uncharted/thumbnails/src/thumbnails.thumbnail.js?:224:12)
at Thumbnail._loadImages (webpack:///./lib/@uncharted/thumbnails/src/thumbnails.thumbnail.js?:158:25)
at Thumbnail._init (webpack:///./lib/@uncharted/thumbnails/src/thumbnails.thumbnail.js?:99:11)
at new Thumbnail (webpack:///./lib/@uncharted/thumbnails/src/thumbnails.thumbnail.js?:47:7)
at eval (webpack:///./lib/@uncharted/thumbnails/src/thumbnails.js?:143:25)
at Array.forEach (native)
at Thumbnails._render (webpack:///./lib/@uncharted/thumbnails/src/thumbnails.js?:137:10)
at Thumbnails.loadData (webpack:///./lib/@uncharted/thumbnails/src/thumbnails.js?:211:7)
at eval (webpack:///./src/StrippetsVisual.ts?:1096:43)
From previous event:
at StrippetsVisual.updateThumbnails (webpack:///./src/StrippetsVisual.ts?:1095:44)
at StrippetsVisual.showThumbnails (webpack:///./src/StrippetsVisual.ts?:1018:38)
at HTMLDivElement.eval (webpack:///./src/StrippetsVisual.ts?:780:26)
at HTMLDivElement.dispatch (https://msit.powerbi.com/13.0.1700.1070/scripts/jQuery.js:4732:27)
at HTMLDivElement.elemData.handle (https://msit.powerbi.com/13.0.1700.1070/scripts/jQuery.js:4544:28)