In Chrome version 69 released this month Google somewhy decided to do something retarded and show disrespect for the end-user's choice, making it by default the only option to have all granted Flash permissions not last longer than current session. This added "feature" became called ephemeral Flash permission. I understand they don't even want to ship their browsers with Flash support at all, but cannot understand and excuse for intentionally creating something artificial to begin directly bother the users while exposing the lone switch to old behaviour someplace nigh inaccessible. Myself I'm much more in favour of Edge giving explicit options to allow Flash and allow it only once.

One may want to go to chrome://flags/#enable-ephemeral-flash-permission and disable this immediately. (Right click and copy link address, Chrome doesn't support website linking to it's settings pages)