Just a guess, but if you are accessing the Worksheet as a View, rather than saving a new View from the the Worksheet Viewpoint, then the View will have a layer setting, even if it is custom, which will hide all new layers that were added after the Layer Combination was last updated, or the "custom" combination was applied to the View. Since an XREF imports new layers, and the Archicad standard for new layers is to assume they are hidden for all current Layer Combinations, until any of those Combinations are updated, maybe all the XREF layers are hidden in your Worksheet View.
What I do, is make a new Worksheet, XREF the DWG, and immediately create a new Layer Combination to capture the current state of the Viewpoint. Then I save that as a new View. Note that some of the XREF layers may still be hidden if they were hidden in the original DWG before the last time it was saved. But you can see all those new XREF layers at the end of your Layer List. (This is another place where the Quick Layers palette can be useful to explore and refine what XREF content you actually want to see in any particular View.)
BTW, DraftSight is an excellent and inexpensive DWG viewer and editor that is available for Mac and Windows. So, it is a great way to see (and get a reality check on) what you are exchanging with consultants who use AutoDesk products.
Ransom Ratcliff RATCLIFF CONSULTING LLC Charrette Venture Group ArchiCAD 4.55 - 25 Autodesk Certified Professional in Revit macOS + Windows