This is an FYI report on a technicality that Charlie requested I post so T3G folks are aware of it.
I have an AGO web map for Maryland geology education (it's at http://mdgeoed.maps.arcgis.com/home/webmap/viewer.html?webmap=d7cfa7a928f14d89ae9556612001033b if you'd like to look at it), and as usual it begins with "http". However, my Chrome browser started inserting a "s", so the URL started with "https". Most layers continued to load, but some layers that came from the web that were just "http" layers now failed to load because once the web map URL is https, it demands that all layers used are also https. I found I could change some of my imported layers to https and they still worked, but some wouldn't work with a https URL. So the main point here is watch out for mixing http and https layers because you might have failures.
Why was Chrome adding the "s" to the http? It seems there is a setting known as "HSTS" that requires higher security, and if a URL gets added to this list in your browser, it will add the "s" to http. You can search for "HSTS" and get more info. A tech person at my school fixed this for me so I'm not sure of all details (maybe you can get to this via normal browser settings, and maybe not), but I think arcgis.com got added to my HSTS list - why or how I don't know - and once we removed it the problem was solved. Perhaps some source that had the HSTS setting for arcgis.com pushed it out to users. So if your map layers start acting oddly, check the URL for the map to see if it has changed to https.
