How to debug "Don’t know how to make a localized variable an alias" errors at startup?

Question

Background: my company provides (confidential) elisp libraries for editing source code in several languages, including TypeScript. I added some lines to load these libraries to my init.el:

(require 'REDACTED)
(require 'REDACTED-typescript)

This worked as expected: when I find a .ts file the company-specific TypeScript mode is enabled and works as expected.

I later encountered a problem, however: when I quit Emacs and then restarted it, desktop would attempt to re-find files I was previously visiting; if any of them were .ts then it would fail to restore my previous frame arrangement and would instead emit the following error messages in Messages:

File mode specification error: (error Don’t know how to make a localized variable an alias)
byte-code: Don’t know how to make a localized variable an alias

It tried starting Emacs with -debug-init, but this did not cause a debugger to open when this happened.

After much futile deletion of content from init.el and removal of potentially conflicting elpa packages I eventually noticed that there were multiple (desktop-create-buffer …) entries in my .emacs.desktop file, and was able to rectify the immediate problem by killing emacs, deleting my .emacs-desktop file, and re-creating my frame and buffer layout. For now emacs seems to be happy to save and restore my desktop even if I have TypeScript buffers open. Win.

But I am at a loss as to how to debug the underlying issue.

• What does "Don’t know how to make a localized variable an alias" mean?

• If it reoccurs (which seems likely), how can I find out what is causing it, when it does not appear to trigger the debugger despite, apparently, causing desktop-read to abort?