I would double check that you are not trying to edit Admin or Standard role as neither are editable. If you are, it's best to create a new role with the same permissions then update the preferences that you desire. Should have no issue enabling/saving this with a custom role.
Here is some extra documentation that will guide you: Managing User Roles and Permissions - Marketo Docs - Product Documentation
This is what I want to change for users (marcom and echannel- both are custom roles with access to Marketing Activities/Design Studio)
Global eChannel Operations Manager
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