re: I have noticed that there are frequently posted conflicts with access manager plugins.
Most of which are old. I can not recall anything recently. The only time there’s a real conflict is when such a plugin hijacks the core WP login process without implementing the required core actions and filters with the correct params being passed to them. This really only affect the Link extension. The s2member issue is a completely different issue.
re: User Access Manager?
I am not currently aware of any conflict with User Access Manager.
As far as I know, the s2member issue is present and is not something I can resolve. That plugin resets all custom roles and capabilities when it updates (at one time). This will break any and every plugin which relies on them, which there are many. For example, small plugins like Easy Digital Downloads, bbPress, BuddyPress and WooCommerce.
Hope that helps!