MGS1600 Not Reading left and right signals correctly

The company I work at has built an agv to move parts from our storage area to our assembly line. We have been starting to run into an issue lately where the agv will jump to the wrong speed after reading the left and right signals on our track incorrectly. The way we have it set up is that 1 right signal is a stop, 2 is slow speed, 3 is medium speed, and 4 is fast speed. The issue always seems to occur when the agv is traveling in the fast speed. It will go to the track position where the medium speed markers are and then only read the first two right markers and then incorrectly go to slow speed. It does not even read the rest of the left marker signal after it reads the first two right signal markers. I know its not a programing thing as far as setting the speed goes because it works when you manually test the tape under the sensor. It will read the markers correctly in ascending order for all speed changes, and it will read all markers in descending order correctly so long as it is not in the fast speed.

I am inclined to believe that there is something wrong with my mag sensor, it has seen its fair share of use in the past year and I worry that it may not be working at the fast speed due to some sort of minor vibration. I can supply the code if that helps any. We are using a MGS1600 v3.1 and a FBL2360 motor controller. Any help or feedback in trying to correct this issue would be greatly appreciated.