Here’s what happened, in a nutshell.
Around Dynamo 2.8 (I think - it was July of 2021 but I can’t track the specific release version) Dynamo started adding the OpenXML based nodes for excel interaction. They have a dependency on OpenXML, a library for working with particular data structures.
Archi-Lab has used a version of that same library since… well a LONG time ago, though I am not sure what for or when.
At first there were no issues as the versions were aligned, or close to it anyway. But to keep pace with other tools Dynamo and or Archi-Lab update to new versions of the library as they both see fit. And as .NET will only let one version of a library be loaded by an application, and once loaded it cannot be changed without restarting the app. This is known as a dependency conflict.
Sometimes the conflict between versions is ok as there aren’t any API changes. This was the case early in the split, and apparently until 2024. Sure, it’s looking for version N but finding version N+X, but the library hasn’t updated enough to matter as the books the applications need are where they have always been.
But in 2025 the library changed enough that the books are in new spots - the API calls don’t align to what they were before. My guess is this stems from the .NET changes which would likely require one or both tools to update the dependency version and now we are too far apart. So when Dynamo goes looking for the OpenXML book where it should be it isn’t finding it, as we are in Archi-Lab’s version of the library not the Dynamo one. The load order could be changed to always load Dynamo core nodes, but that would break Archi-Lab instead of the OpenXML nodes.
Likely not much work on Konrad’s end, but that work isn’t part of his job, and he has a lot more fun stuff to do in his personal life than he did when Archi-Lab was underway. The Dynamo team could likely integrate the Open XML library in a different way so as to harden the system against this type of issue, but that opens up different problems and shouldn’t be done in a hurry. They also can’t back ship int Revit readily (need an update to 2025 that is major enough to push a new Dynamo build, which isn’t likely as we are nearing the half point of it’s lifecycle), so the fix is easier to deploy to users via the package.