You’re not really specific enough so I make some assumptions based on experience. Used autorouter to route traces to length, not manual layout tool. All traces routed at same time, not in stages. Out of length traces are too short, not too long.
First check setting kbak shows. Also ensure length drc is set to on. If traces are in center of group they may have been added last and had no room to expand, equal length would have been ignored.
Here is how I deal with this; rather than use the tolerance check box I find the longest trace then subtract tolerance to get min and max limits for that class. Using tolerance allows longest to keep changing throwing off the group skew as you work. Next use net length monitor to find trace that is furthest from target, will usually be in center of group. Push other traces away to give room. Some tuning will go away as you do this. Once the shortest has snapped to length, start picking pin pairs from center out in each direction then right click and tune to length.