V4 file read in to V5 error not seen before.

Loading a V4 model into R26.3 and getting error not seen before;  'As there are too many workspaces, their number has been reduced'.

Does this mean it deleted workspaces, which ones, how do I determine which?

As a subtier for many different customers who have a wide variety of data and practices we see this often.  In V4 .model files the 3D CAD and 2D Drafts are both resident.  Rather than catalogues of 3D and 2D documents they often have a stored library of files within the document that are called “dittos”.  These are drawing symbols, hardware, parts, fastener vectors, drawing templates, etc. and even when not used they are rarely cleaned.  Sometimes, a ditto contains other dittos.  For each ditto, a separate workspace exists (it can be either 2D or 3D).  Separate workspaces also exist for the 3D Masters (products and parts) and 2D Drafts (drawings).  When you open a V4 file in V5 when multiple workspaces exists some may be eliminated.  I’ve never found a pattern as to which ones are eliminated but can confirm that I’ve seen drafting sheets be eliminated when opened in V5.  I would recommend reviewing the file in V4 for verification that the relevant engineering is available.