Make sure the right membership tag is applied to a test contact’s record that you’re testing. You can verify what the correct tag is for your membership levels by going to (in the wordpress admin sidebar) Memberium > Memberiships and make sure the test member has the correct Infusionsoft tag applied to their Infusionsoft record.
In general, Memberium is compatible overall with all themes. Some drag and drop themes may disable some functionality, such as Excerpts, however that capability can be recreated within the theme itself manually using shortcodes. When using Memberium with LearnDash, there are some additional restrictions. There are a variety of themes you can choose from that work well with LearnDash, depending on your needs.