The problem here is your base dashboard is to heavy to load, so it either needs more memory / CPU, or you need to create a very basic dashboard with just one widget on it. Not ideal but you could then look at our post on setting up Metabase and Surge. your dashboard (Surge Mautic Dashboard into something Amazing!).
For the moment go to your dashboard with import at the end and make a basic one https://yourmautic.com/s/dashboard/import
Let me know how you go