BuddyPress.org

Hello!
Very new to buddyypress, fairly novice with the technical stuff so hopefully someone here can pick up what I put down.
So recently installed buddypress, latest version, wp and theme (Lambda theme) and all plugins up to date – no problems. Upon activation of buddypress, I get a 500 error. Went through the usual route, disable all other plugins, still 500 error, switch to 2017 theme, everything works, activate other plugins and still everything works. So I thought no problem, theme isn’t compatible with buddypress I will move on.
However, I had the same theme on another install so tried buddypress there – worked fine. Back to the original site, turned on debug , and found this:
Uncaught Error: Call to a member function get_primary() on null in /home/travellingnz/public_html/wp-content/plugins/buddypress/bp-core/bp-core-functions.php:2558

Upon arriving at the aforementioned line 2558, I came across this: $bp_menu_items = buddypress()->members->nav->get_primary();

Now if I remove that line, site runs fine, though the buddypress menu items are missing, add that line back and the 500 error returns.
Again excuse my technical virginity but is there something I can just add or take away from that line of code so that everything works or is there more to it than that? Appreciate any advice.