Work was done in Illustrator 25.2.3 under Mojave 10.14.6. A screenshot showing the fill separated from the outline as well as a simplified/de-branded version of the 5-up document with only the problem art and a section of non-problem art (for relative position reference) left in place are attached.

In Illustrator, the customer's AI file was opened and stepped 4 times to produce a 5-up document (as has been done countless times before on similar files). The resulting 5-up file was saved to subsequently be imposed in Prinergy. All artwork was duplicated perfectly in the first 3 copies but in the 4th copy (5th position), on the "500" (and only the "500") the fill appears to have shifted to the left, though the outline shows as being in the proper location. Clicking on the 5th blue "5" in the AI file results in the path being highlighted as shown in the screenshot.

I'm guessing the resulting AI file is somehow internally inconsistent as selecting that 4th copy with the fill shifted and simply copy/pasting it to another location magically results in the fill of the problematic 500 "snapping" into alignment with the outline even though no operation that should have modified it was performed. In fact, when proceeding to undo that copy/paste, though the pasted version disappears, the "snapping" of the fill to the outline is not undone and the silently-fixed 500 remains corrected. Once it has fixed itself in such a manner, reverting to the original file is the only way to get the fill and outline back out of sync.

Unfortunately, going back to the original artwork and repeating the process in attempt to reproduce the results has not been successful - the operator did not notice the shifted fill prior to saving the 5-up version of the file and cannot state with certainty whether or not it was correct on screen after completing the stepping but before he saved the file. Therefore I cannot pinpoint whether the issue occurred at the time the 4th copy was placed or if it was the result of something happening in the save process - either way the file that was produced was problematic and prints with the 5th "500" out of position.