Hello there,
Click the rebar that does not change (once), select “edit constraints” from the upper right menu on the ribbon, and constrain the rebar parts to the edge of the columns or to the rebar cover. It should work.
If you click blue dots … for every side of the rebar … you can constrain those sides to edge or rebar cover(dotted line). In the picture, you are constrained to -221.0 from the edge, you can click the blue symbol near the blue arrows and switch it to rebar cover (dotted). Now if you modify a column and the dimension of a not constrained rebar changes … the rebar does not change.