May be a long shot, but also look at other things that write to the tags in the GRT instruction. The values shown on your screen are the values at the end of the scan, but they could be something else while the GRT is being evaluated. To isolate that, add a couple of MOV instructions on a new rung right above this one that MOV the tags to new, otherwise unused locations.
The same holds for the tags on the OTE instructions. Do a cross-reference on them and look for additional places where they're used destructively. Something else could be writing them ON.