New Issue w/Web Maps

[BrianO_keefe]

So all of a sudden, a nice batch of our webmaps are crashing... but not all of the time.

They are providing the following type of error message:

"The layer, <insert name of random layer>, cannot be added to the map."

However, if you refresh, suddenly that layer loads just fine but another one won't load. But a refresh might bring back issues with the last layer or it might load perfectly?

We have checked fiddler, Google Developer Console, and the best I can tell is it keeps spouting on about a Syntax Error...

SyntaxError: Unexpected token <
at Object.b.fromJson (init.js:131)
at Object.json (init.js:84)
at r (init.js:88)
at c (init.js:103)
at d (init.js:103)
at b.Deferred.resolve.callback (init.js:105)
at init.js:92
at k (init.js:107)
at t (init.js:107)
at d.resolve (init.js:109)

I'm lost. We've troubleshot everything I can think... 

If you want to take a look, here is one of the maps... ArcGIS Web Application 

[KellyGerrow]

Hey Brian,

Are you able to share the web map? 

-Kelly 

[BrianO_keefe]

Here is the original map. It has worked fine for almost a year but suddenly it stopped.
ArcGIS Web Application 

Then I went in and recreated the MXD, published a brand-new REST service from it, created brand-new AGOL objects (feature layers) and a new AGOL web map, opened WAB and added the map, then published the brand new version of the above map as this:

ArcGIS Web Application 

[ChrisWhitmore]

Brian O'keefe‌ - have there been any recent changes to the server? It appears requests are sometimes returning a web adaptor error:

[FelixPertziger]

Same issue here some 2 of my 7 maps show:

I can see nothing missing in table of content, but still don't like this message especially when multiple syncs failed and suddenly went through this morning. Health board says all fine.

[KellyGerrow]

Hi Felix,

Can you share your web maps? Also, please get in contact with technical support so we can look into this further.

-Kelly