Symbology disapearing on Feature Layer

[Jean-SébastienRoy]

I'm looking for any reasons/causes that would make custom symbology defined for a published Feature Service disapeared after some time ("Feature Layer", not "Feature layer (hosted)").
So far I know the underlaying data was not changed between the setup of symbology and its disapearance.

What was done : How To: Limit access to secured hosted services or map services in ArcGIS Online for public-facing w...

Create new feature layer from an "hosted" one, limit the URLs able to access the resource and store credential with the service item

On the new layer (that is public), set the visible zoom levels + symbology + custom popup using Expressions (+ save changes!)

Refer to the new layer through the javascript SDK to display in a map (readonly, no editing done, just getting the data and making queries)

Somehow the symbology was lost after a few hours/days (not sure about the exact scenario, the client says nothing was done to the layer in between..)

This is where the symbology was modified on the layer (access the layer + Visualization + Modify symbology + save)
Where the symbology was modified

Thanks in advance for any clues..!

[RussRoberts]

Can you check the activity report for the org to see in the logs if there was any content changes to the items? 

[Jean-SébastienRoy]

I'm not in that organisation, working as a consultant, but according to the client no changes where made to the data, but since my post, they did not report any such change, so it might still have been the reason behind all that, thanks!