I'm seeing this as well when attempting to run an optimised Python 3.8 build on an old Debian 9 system (with the curses and socket extension modules).

For example:

cpython/Modules/socketmodule.c: In function ‘PyInit__socket’:
cpython/Modules/socketmodule.c:8304:1: error: the control flow of function ‘PyInit__socket’ does not match its profile data (counter ‘arcs’) [-Werror=coverage-mismatch]
cpython/Modules/socketmodule.c:8304:1: error: the control flow of function ‘PyInit__socket’ does not match its profile data (counter ‘time_profiler’) [-Werror=coverage-mismatch]

That said, I did install missing optional dependendencies and then do a reconfigure without doing a "make clean", which is pretty dubious.

So David's assessment here sounds good to me: the bug is that "make clean" should be removing the intermediate PGO files, but is currently leaving them lying around.