Whenever I try to Register via the My Account page, it registers an account but sends me to the WP-Login page with the message “Your session has expired because it has been over 180 minutes since your last login. Please log back in to continue”. Why is it doing this?
please temporary switch to default WordPress theme and check, will this problem appear while default theme is active or no?
In addition please provide us with admin credentials for your site in private content.