I see that it's possible to enable snapping when adding a new feature in AGOL (by holding down the CTRL key), but I cannot figure out how to snap existing features.
I haven't tried in a while and actually it just worked for me! I do use Chrome, and my current version is 66.0.3359.139 (Official Build) (64-bit). Is it possible that I had the version you mentioned when I posted my question last month?
Can you tell me what web browser you are using to access ArcGIS Online? I ask because we have a bug logged for this same issue when a user is working with Google Chrome version 55.0.2883.87.
If you are using Chrome, can you switch to a new web browser and try it there? You should be able to use the same CTRL key to snap existing points and lines in ArcGIS Online.
If the failure is only in Chrome for you and things work fine in other web browsers, I'd recommend that you contact Esri Technical Support at 888-377-4575 so that we can create a case for you on this issue and add you to this bug.
That's good news! It is possible that you were at that version and the issue has been fixed on our end in this later version of Chrome. But yes, I would say you were running into that bug. Glad things are working as expected now!
Retrieving data ...