I’ve experienced this problem over and over again…
Funnelish Automation > Although I switch on ‘Send to optin email instead of Payer email?’, it seems to be turned off the next day when I want to edit the automation just to see if it’s still on or off.
Is this a known bug?
Interesting 
It’s certainly not a known bug first time hearing of it, but the only viable explanation for it is that you were logged out and your changes weren’t saved correctly, or something happened preventing them from being saved other than that nothing else should affect your own automation settings…
Similar bugs could happen in the current platform, that’s why our team is preparing to roll out a full rewrite of the platform next couple weeks to get most of the user experience stability issues resolved or avoided.
For the time being, can you try to save your changes when you create/edit your automation and then refresh your page to see if they are saved correctly?