Assuming you have a stable network update your device.  Then delete the app and download it again. When prompted select “Join existing system”. Follow and accept all promts and finally sign in with your credentials.

Did all that, still continuing to ask me to login even when I am

That can imply that the account you are logged in as is not the account the system is registered under.

Question…

I noticed the app will flash “sign-in” upon opening; but quickly goes away. Is that what is occurring?

If so, I wouldn’t be too concerned as it appears to be a security measure while the app does a verification. As long as you are not prevented from making changes to your system (like setting up group for instance) then I wouldn’t sweat-it. 

Is there away of just resetting everything? As I’ve reset app, phone, speaker

Time to call Sonos support and have them look at the details we users can't see.