That’s smart, some people love scanning QR code, like they think that they are winning the lottery or something if they do the scan 
; but good let’s use this to make them join the community 
Push notifications are going away if you disconnect. And people don’t necessarily subscribe to threads to get notifications.
Possible solutions to make people come back:
1° Make the main calendar for your club only available on your discourse page and as your members don’t want to miss real life events they will be forced to check it and at the same time view some recent content and participate.
Root cause : many people cannot properly configure their mailbox and are losing an essential tool for daily organisation that discourse was very right to be built with. There are people that are very grateful that I showed them how to create mailbox rules hence the following could be an interesting experiment :
2. You could reuse your real life promotion strategy by asking people to which categories they would like to subscribe and tell them how to create a main mailbox filter.
Tell them that they will only receive emails from those categories + those they answer to and that each month they can comfortably check this specific mail folder. There are many forum members like me who for certain communities like to roll that way except for direct messages or topic I open, then no filter is necessary.
I don’t like to be reminded that I am a member of a ping pong club every day, even every week, however checking it out when I want it(except for certain chosen categories like events or for replies to me) is the way I go.
Let me know if you try this bold move 