Hi Raphael,
Thank you for bringing this to our attention! As far as I'm aware, this is an unintended regression and not a deliberate change. The process of preparing 2.7 (with 2 different versions of Bootstrap and every single template in AtoM) was complicated, and coincides with a gradual internal transition of how we maintain and develop AtoM at Artefactual (see the original Maintainers announcement
here) to a new team. All of this churn meant that some regressions have slipped through - so we appreciate help from the community in finding and addressing these!
I have filed a bug ticket for this issue here:
Hopefully our Maintainers will be able to investigate before the next release! In the meantime, remember that the Advanced search menu has a repository filter, so while it is less convenient, you can still scope your searches to one particular archival institution using that filter.
Cheers,