An issue may occur whereby the Groups tab disappears from the My CRM area, despite the user having rights to use groups.
The Group Access option under Administration -> Users -> Users was set to Yes, and the tab was not being hidden.
The captions can be edited by navigating to Administration -> Customisation -> Translations and searching for the 'YesNo' caption family.
The issue was caused by a change in the caption codes for the translations in the 'YesNo' caption family.
These should be Y for Yes and N for No.