From the 28.1 NEWS file: this seems to be a breaking change:

** The WHEN argument of 'make-obsolete' and related functions is mandatory.
The use of those functions without a WHEN argument was marked obsolete
back in Emacs 23.1. The affected functions are: 'make-obsolete',
'define-obsolete-function-alias', 'make-obsolete-variable',
'define-obsolete-variable-alias'.

which if I am not wrong probably caused several of emacs-* packages to FTBFS in the mass rebuild.

(Unfortunately the build.log's only refer to the line-number in the elisp files: dunno if that can be improved?)

Jens