I confirm the issue with URE Settings page, if plugin was activated for single site of multi-site WordPress network.
I need to refactor code logic, something like this:
1) Network activation: The only URE Settings page under Network Admin Settings, all settings are global for the whole network.
2) Single sites activations: Every site has its own URE Settings page. Additionally, under Network Admin settings superadmin may input license code – one time for the whole network.

Thus current version does not allow to use Pro version as the single site activation plugin. Thanks for the help in discovering this bug.

Licenses are counted for the WordPress installations. One WordPress (including multi-site one) installation requires one license. So Personal membership is enough.