Adobe Ilustrator - Links compatibility Windows and Mac

What Mac OS are you running? Try both Catalina and Big Sur. Is your server using afp: file sharing protocol or other less compatible smb3: nfs:?

Adobe out of best practices has for many years suggested not to use networked drives and removable media, but that is not possible at a large agency. I have worked fulltime everyday for the last 30+ at over a dozen companies and consulted as a contractor at 100s more.  Overwhelmingly in most places  this works fine that links hold on .ai file created on an opposite platform. The problem existed more in the 80s & early 90s and what resolved the issues then was:

1. Upgrading the server software
2. When Mac OSX first  came out, was popular to have •bullets in filename, but that made files invisble
3. Removing and nonalphanumeric characters on folders & filenames  (especially :./) dashes underscores and parens are ok.
4. Checking the settings on your server software usually windows to be more compatible with mac.
5. never keeping more than lets say 100 images in a folder, as that can slow down performance

Strange that something new has developed, until a new server or ilutrator patch comes out you may wnat to run an older verison of .ai.

If all your images are in one folder, you could move the .ai file into that folder, and illustrator while opening a .ai file looks at neighboring files to relink.

Although it may have worked in the past, placing linked files from a networked drive isn't recommended:

• "Saving files on a network drive or placing linked files in Illustrator from a network drive can slow down Illustrator, or corrupt your files. Additionally, you can receive the error, 'Could not complete the request because the file is locked,' or 'Could not save because of a disk error.'"
  -Illustrator support for networks and removable media

Instead, you could try adding your linked assets to a Creative Cloud Library and placing them from there.

• Creative Cloud Libraries