With the help of ChaosGroup, we have identified the problem.
It will be fixed on the next Forest update (planned for the next week).
Problem was caused by a bug of Edge mode with Surface Areas, but it was not detected until now, because some optimizations added to V-Ray 6.10.01. Other areas (as Spline) work fine.
Unfortunately there is not a workaround, except to downgrade V-Ray to the previous version.