We did the 5.1 upgrade on Wed/Thu and, while it was generally smooth, hit a couple of bumps - although we had the same demo on master from a couple months back, so somewhere in between 5.0 and 5.1.
Our flow is a bit different because this deploy is Kubernetes/docker based, but we did find that the new project package.json seemed to just pull in the archesproject/arches#5.0.0 package without its dependencies. I had assumed this was down to the approach we were using, but might be related? Our workaround was to use the package.json in the root directory, and that solved our issue for the moment (specifically, d3 expected to be under a dist folder in the new version, and giving a 404).
As a side-node, we came across one or two other upgrade issues - in particular, reindexing ES threw an exception (concept relation not found in concept_types.py:68) - again, I'd put this down to how we had done the upgrade so didn't want to add noise, but if it'd be useful to file a more detailed report, can do.
All the best and thanks for all the hard work on the new release!