Cannot sync all photos

I've just gotten access to a spare iPad Air 2 at work, running iPadOS 15.8.3. Trying to sync photos from a 2019 MacBook Pro (Intel) running Sequoia 15.1. No beta Apple software in use.

I have just over 17,000 product images that I need to copy to the iPad. I've converted them to a small enough filesize (using Adobe Bridge Export) to all fit in the available storage with a couple of GB free. All images are sRGB JPEG files, stored on the internal SSD.

I cannot get the Finder sync to copy everything. I've tried:

Rebooting both iPad and Mac.

Syncing the image folder, importing to Mac Photos and syncing the individual album, syncing the entire Photos library (there are no other photos in it or on the iPad.)

Tried turning on and turning off manually manage music (no media besides photos is present.)

This iPad was just wiped and restored (using the same Mac) so the software is brand new.

Both iPad and Mac are signed into the same Apple Account.

The Mac is running Sophos Endpoint AV but this doesn't seem to be a problem and I cannot disable it anyway (corporate machine.)

Neither iPad not Mac is throwing an error, it simply won't sync all photos.

I'm using a USB-C to Lightning cable which seems to be working, direct from Mac to iPad. The photos that do sync copy pretty quickly. Switching to a USB-A to Lightning cable via USB-C dock makes no difference.

I'm using an admin account on the Mac.

I use Adobe Bridge for organizing, cataloging, and metadata operations on the Mac and Photoshop for editing. This is not a new workflow and its pretty efficient (I've been at this job for 10+ years with the same tools.)

I've gone round and round with this. Finder sync isn't working, Airdrop isn't working, nor Apple Configurator (I don't need the iPad managed, as I'm the only user, but it was worth a try) to transfer everything. Breaking the large library into smaller folders has helped, and checking "Include videos" as well (even though its all JPEG files.) Still at it. Repeated syncs will sometimes randomly copy more images.

Final tally is about 900 images not transferred out of 17,000.

Meanwhile, I've abandoned iPad Photos and downloaded HashPhotos. This is similar to Photos but has many more features, including Sort by Title which I need, date is useless as I work with specific products and not "memories." This has at least taken care of the viewer requirements.

Finally, I'll mention that I'm a longtime Apple user (almost 30 years) who personally owns three iPads. I've used Photos before on my personal gear to sync finished JPEGs with my iPads/iPhones and its always worked. I'm also a former Mac Genius and currently a working pro photographer so I'm pretty confident about my technical approach, but apparently doing something wrong. I need to know what I'm missing here.

TIA for any help.