This has been a known problem for many years, going way back to the Pro|Mechanica days. I have encounter this many times, and I have submitted tech support calls, and tech support has never been able to resolve it. The only answer I got back from PTC was if you put pre-defined measures in your model, use the values in the run summary window and not the fringe plot.
If you're on maintenance, try submitting a support ticket. If not, upload your model, and let some of us trouble shoot it, if you're allowed too.
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