Gantry position feedback check on Ethercat

There is a setup of Indradrive Cs with MSK servos for 4 axis machine via SoE. There are two Y axis joints.
Lately I have experienced rather awkward situation, when one of the Y joints suddenly changed feedback position. Perhaps a M1 encoder multiturn issue, but I can not be certain. It is being investigated.

Now, is there any possibility to check within HAL setup a difference between both joints feedback? In case there would be a difference (e.g. 0.5mm), I have in mind a stop of the machine.

No need for hal--- just switch from world mode to joint mode, DRO shows both Y values there.
If they do change, se how much, see what joint is causing it, then use halscope if you need to find out exactly what is going on.
Edit:
Things that can cause that on tandem joints/axis:
Raked gantry
Rails not parallel
Encoder rust/wiring/interference
Encoder power marginally low or not clean
Mechanical issues binding/dirty rack-pinion/ loose bolts, loose motor-gearbox, to much pressure on rack, stripped belts, etc