If you’re logging in on multiple devices (say you have SC on your phone you log into it on an ipad), SC only stays logged in on one of the devices. Everything is saved, the only problem is it’s annoying to log back in, so you’ll have to stay on your phone only.
If it’s not that, it’s probably a bug. Give them a review on the play store about it or find a way to send them a report.
Also, is there any way someone else knows your password and is logging into their device?