When you are working on a big project, once in a while, Revit gets tired off doing all the calculations, all the coordination and shows its anger on simple families that have instance parameter grips.
For eg., here is a very simple extrusion family with an instance grip.
Pulling the grip after working on the project for some time would not change the geometry of the family. If you go to the properties of the family and change it’s instance value, it works fine.
But still, one cannot pull the grips to modify.
However, if you use the align
command to extend (change) the geometry, the grips become alive again!
I don't know why this happens.