Team Member profile settings are tied to the Username of that team member. Changing the Username breaks that relationship and results in the team member losing any grid customizations, filter applications, personal default report settings, sorting, visible columns and items per page.
This can be helpful in cases where a user gets an error on a grid where they have a filter applied that is a broken filter. This can happen if the filter is applied for an attribute that has been deleted or changed, or a workitem that has been moved, changed or deleted. It is a rare occurrence, but it can happen. In those cases a Profile reset is usually the only solution, but ti does mean that user will lose their settings.
If this happens there is no way to recover those settings. The team member will need to recreate them as they go.
If the team member saved their views (My Views in Digital.ai Agility) then they can easily reload the grids to their previous state.