Potential bug: super fine line around shapes that are filled white

Hi there,

I see weird lines around white objects that drive me crazy and I am wondering if this is a bug. Is anyone seeing similar things?

I am working currently on updating a museum map. Various exhibition rooms have various colors. Walls are compound paths that are filled white. The white compound path sits on top of the filled-in rooms and hallways and stroke setting is transparent/0 width.

The original plan is over 10 years old. Just last week, I was working on it and it looked like expected.

The map is placed in an Indesign document. Today, I exported a PDF-X4 file for offset printing like I always do. When I checked the PDF, I noticed super thin hairlines around the white compound paths. 

First, I thouhgt it might be a display error. But when I check the color channels (Acrobat output preview), I can measure them. And when I render the PDF page in Photoshop, it does render these super thin lines.

When I zoom in thouh in Acrobat, the lines do not seem to scale. Whatever the magnification, the line stays super thin. 

My guess is the lines won't print because of how thin they are. But it's super irritating and I want to be more confident in telling my customer that this will not cause a problem.

I'll attach two screenshots. The first shows a corner of the building, rooms in gray, and a very thin pink line around the white compound path. Magnification 125%. The second screenshot shows a zoomed-in corner of the same area, upper left, with the dotted line for orientation. Magnification here is 3200%. 

I am confident that there aren't any objects in Illustrator that have a stroke color assigned to them. But even in Illustrator, I can see the line. I've updated to Illustrator 29.3.1 seven days ago, Mac OS 15.3.2

I am puzzeld. Thanks for any ideas what's causing this.