Without knowing the model and type of DRO, I would suggest that your first step would be to test the DRO itself for any problems. Use a dial indicator on tha carriage and compare the readings to the DRO. Watch for changes in the DRO reading after you stop the motion which would indicate some binding in the scales.
If your DRO is OK, then look for ;
1. Loose gib adjustments which will cause the table to rock from side to side
2. Looseness in the brackets that hold the brass acme screw nuts
3. Inspect the thrust bearings on the lead screw for any contamination or looseness.