“Enable s2Member’s Auto-EOT System?” option is keeping come back to blank

Hello,
I have a problem for a few times now with this setting “Enable s2Member’s Auto-EOT System?” , I choose the option “Yes (enable the Auto-EOT System through WP-Cron)” but when the time pass and we notice the member EOT start not to work and I came to check this setting again and it always go to blank ( not choosing any option )

I’m using a free version and wanting to try to reinstall the plugin but I can’t find a way to save my settings.
The menu for Export/Import setting is not visible for me , maybe it is only Pro version function ?

Please help.

Thank you.
Kanniga