Theme reverting to default blue

Hi. We have recently (in the past week) noticed an issue with our branding in the Connections app within MS Teams desktop and web, where our custom theme keeps reverting to a default blue colour. Refreshing the page does not fix the issue. Our chosen theme only reappears when a user navigates to another tab (e.g. Activity, Chat, Calendar) and then returns to the Connections tab.

The colour theme works as expected when accessing Connections outside of Teams (e.g. via SharePoint).

Has anyone else experienced similar issues, or know a potential cause/fix?

Thanks.