The issue is related to Chrome, and their step-by-step plan to deprecate Flash. Here is an article that explains such behavior:

According to the article, since October all sites will require user permission to run Flash. As you might have visited it was added to your whitelist automatically. Now the eMags are published to, and you need to add this website manually by going to chrome://settings/content/flash and Click Add under Allow option.

I understand this can be frustrating to your readers, but unfortunately, there is nothing we can do. You may either instruct your readers how to add new sites to whitelist for running Flash or try sharing eMags via not secure http:// protocol. The second option may work for your readers as was cached.