Sorry to hear that.
This could be caused by a new Shield’s v19.0 “User Session Lock” feature.
But to be sure, this is what we recommend:
- Reproduce logging out
- Use a forceoff method outlined here
- Log into your site
- Go to your Activity Log and filter logs by your IP address or username.
- Review logs. Hopefully, these will tell you why you’re logging out so you can change Shield settings to prevent it from happening again.
Let us know how you get on.