The issue I believe is the layout is or was set to INCHES in a METRIC drawing, as such it was having a hard time doing the viewport annoscale math.
Thank you! Thank you! Thank you!
That is exactly what it was! We have a metric job, and use an A1 titleblock, but usually print half-size and do not have any A3 printers, and so squeeze it to fit onto 11x17 paper. When you select 11x17 paper, the default changes to inches, and you have to remember to change back to mm before you save it to the layout. Oddly enough, it prints OK, and it is not until the next regen that your labels have shrunk.