I mean, there was a problem, but I think ‘Catastrophic’ is maybe overstating it.
It did lock Excel and force a Task manager exit, but reopening from an untrusted location (so macros didn’t run) let the file open fine.
Its a shared workbook so in a way they deserve whatever they get, but actually nowhere in the Excel documentation does it say ‘Don’t use this feature is unstable, always has been’.
I’m just waiting to hear if unsharing, cleaning the VBA and resharing has fixed it.
No word as yet so I think we can take that as a ‘yes’, or at least a ‘very probably’.