Ok thanks Chris. I appreciate your quick reply.
I spent most of the day on this so I thought I’d share the solution in case anyone else experiences this.
Turns out the issue was unrelated to the plugin but was with the theme folder name (too long and needed to be changed). I found this post: https://wordpress.org/support/topic/not-able-to-save-custom-menu-selection?replies=6 and it worked for me.
Thanks.
Did you ever find a solution to this?
I have the exact same problem.
Thanks.