It is possible that the robotic arm might not move smoothly. Here's how to correct that.
There are three basic conditions that could cause a "hitch" as the robotic arm moves over your target.
The first condition would be that the arm is adjusted all the way down on a substrate that is thicker than normal, and you're getting too much friction for smooth arm movement. Place the substrate you wish to measure under the edge of the base of the arm and move the arm assembly down till you just encounter slight resistance when trying to pull the substrate out to the side.
The second condition would be that the arm isn't sitting square on the three posts that hold it in place. It is possible to mount the arm but not have it level when placed onto the posts. Unlocking the rear latch on the arm, taking the entire post and arm assembly straight up and off the posts, and then reseating the assembly on the three posts taking care to have it straight up and down when replaced. You will want to make sure that the latch is fully engaged (parallel with the front and rear edges of the table) when you replace the arm assembly.
And the third condition is the most unlikely one, but possible. This would be either that the mounting posts had become less than straight up and down, or your iO table bed has a warp in it. The bed would be simple enough to test with a level, and the mounting posts could be verified with a t-square or some other known 90 degree angle. If you have a bed that isn't level, that usually is due to a table or surface you've set the iO table on top of that isn't level.
If you should hear a loud chattering and the arm is moving erratically, then that is a fairly clear sign that you have a physical malfunction inside the arm assembly itself. At that point we would ask you to download i1Diagnostics 4.1.2 software and test the iO table. At the end of the test, you will get a PASS or FAIL result. Please save the log file that will result when you go to close i1Diagnostics software. It will be an important part of the diagnosis.