Custom externals return "No such object" errors in standalones but not Max itself.

I have some custom-built externals which work perfectly fine in Max itself, but whenever I try to build a standalone with them I get "no such object" errors. I have tried including the .mxe64 files themselves and tried including the folder they're in. I've tried putting them in the main Max externals folder. I've tried building a collective instead of a standalone executable. I have verified that the .mxe64 files are actually present in the resources folder of the built standalone, but it just does not seem to matter (and I have tried manually moving them to the resources folder even though they already exist there). The strangest thing of all is that out of all the countless times I've tried to build, it actually did work maybe two or three times when I saved the patch as a project first and then built it. But I can't get that to work anymore now either. I have verified that it acts the same way on a different computer.

I feel like I've tried everything. Any ideas what could possibly be causing this?