$sig is just a scalar I use to determine when the loop should stop.

until ($sig) {
    # do some stuff
}
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I declare $sig earlier with our in attempt to disqualify any scoping issues as the source of problems. I'm going to try it on another box with the same set up and see if I have the same issue.

Update:
I tried it on a different server running the same OS and version Perl, with the same result.