Imported Illustrator file leaving "remnants" around page?

[creative_pirson]

Coworker is having an issue in InDesign 2025. They have a file in Illustrator 2025, all black strokes. When the files is imported and placed into an InDesign document, it is initially fine, until it is scaled down to fit the page, then if the bounding box is moved around the page, it will start leaving little pieces of the drawing behind that can then be selected and have to be deleted on their own. The majority of the graphic remains selecteable as a single imported image file. I have confirmed that it is being imported, not copy/pasted or dragged in. Saving the AI file as an EPS does fix the problem, but we've imported native AI files into InDesign for a long time, wondering what the problem might be.

The Illustrator file was a DWG blueprint sent to us as a PDF, then imported into Illustrator to be edited. All strokes, not converted to outline. 
I believe the InDesign file initially had been created with PDF2ID, as its an older form that needed to be updated after no live files could be found. 

[James Gifford—NitroPress]

My experience in this area is extracting complex charts from former print PDFs and reducing them to reprintable form (with updates), saved as AI files. I often find that conversion from PDF, DWG and other formats leaves "loose bits" that may make sense in the original format or are otherwise invisible or unimportant duplication of elements.

After I clean up the PDF page (deleting existing text, framing lines, etc.) I take care to view the page in outline form, where such "invisible" bits often show up. (And can be a real PITA to delete, as I haven't found a good way to identify them in the Layers listings.). I then group the remaining — desired — components, center them on the artboard, and often scale the whole thing up for convenience.

I'd suggest that somewhere in your process, you aren't doing quite enough cleanup/grouping, especially the step of looking for stray bits and grouping the result so it's handled as one element. But I am maybe journeyman in Illustrator; more experienced users might have better insights.

Also: a common tool/platform in the CAD world is Bluebeam, which is popular and beloved because it greatly simplifies making PDF versions of complex files from ACAD/Revit/SolidWorks etc. In my experience, though, it's one of the worst PDF creators, and I've seen problems and complaints about its output both in this forum and others. All of the above is probably compounded by "crummy PDF" issues — so add a cleanup or conversion step to your process, opening it in Acrobat DC and re-saving if nothing else.

[creative_pirson]

I'll forward this along. But what could cause the stray bits to remain selectable when the rest of the files comes in as a single object?

[James Gifford—NitroPress]

Not a clue, from the description; I'd have to see a sample file/s to nail it down. But any time you have images that start with a poor, nonstandard PDF export, you're going to get problems, some of them downright inexplicable. Unless you can export to an Acrobat-standard PDF in the first place, some cleanup and 'regularizing' effort is going to be needed, whether the goal is a distributable PDF without faults or re-use of the image in another app.