Hi Priscilla,
I suspect the issue here is related to some major refactoring of the Header/Navbar and Admin Sidebar that occurred between 7.6.1 and 7.6.2. See this PR:
https://github.com/DSpace/dspace-angular/pull/2676We don't normally make major changes to site layout in minor releases. However, in this situation, this was the only way to fix some major accessibility issues with the Header, Navbar and Admin sidebar.
Unfortunately, though, this means that it's *likely* any custom themes will need to be updated to align with this refactor. This should be a one-time fix (as we won't be doing further major refactors here), but it is an annoyance with the 7.6.1 to 7.6.2 upgrade. One way to possibly approach this might be to start with a "fresh" theme and slowly copy your customizations back in to ensure you can arrive back at a theme that is updated to 7.6.2.
Hopefully that helps gives some clues as to what may be going on.
Tim