Today I tried the buildingSMART validation service with an Archicad IFC exported file (from Archicad 27, but I don't think it's version specific). And one of the errors I receive is about the strict requirement of any Length to be positive (greater or equal to zero).
However, when you export all Archicad properties into the IFC, it also contains the elevation settings, which (inside Archicad) can be negative. E.g., a negative offset of the top of a slab versus the linked storey. This is exported as a negative length, which is NOT valid according to the IFC schema. But it is a very common modelling approach in Archicad.
See WR22 on the following page:
https://ifc43-docs.standards.buildingsmart.org/IFC/RELEASE/IFC4x3/HTML/lexical/IfcQuantityLength.htm
And this is the answer from the validation service.
You can test for yourself on this page: https://validate.buildingsmart.org/dashboard
Operating system used: Mac Apple Silicon
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