This is a warning (Line 201) generated by the OpenStudio SDK - not the Application or SketchUp Plugin. These checks were introduced about 18 months ago - see PR.

Based on edge counts (Line 255), OpenStudio is trying to determine if a given space is enclosed (i.e. a valid polyhedron). If indeed enclosed, each surface edge must match another surface edge, i.e. have the same length, yet with shared edge vertices in reverse order (vs the other). That simple edge count becomes a tad more complicated when dealing with collinear vertices along one edge (while absent in the other). OpenStudio is attempting to solve this mismatch by adding (Line 296) missing collinear vertices where needed.

If OpenStudio fails, there should be follow-up "Polyhedron is not enclosed." warning (Line 205) popping up. Is there? If not, it would suggest OpenStudio has successfully added required missing collinear vertices for its internal checks - no worries.

In addition to this last check, you can always validate the EnergyPlus reported zone volumes (e.g. in the generated run/eplustbl.htm file, under Performance, Zone Summary). A 10 m3 somewhere usually means EnergyPlus has come to the same conclusion about a non-enclosed zone (check the generated run/eplusout.err file for related warnings).