unicodeobject.c has a static pointer to a unicode name CAPI capsule:

   static _PyUnicode_Name_CAPI *ucnhash_capi = NULL;

The capsule is initialized on demand when the parser encounters a named unicode representation like "\N{digit nine}". Once the capsule pointer ucnhash_capi has been initialized, it is never reset. Not even a full interpreter shutdown invalidates the pointer.

A shutdown of the main interpreter with Py_Finalize() renders the pointer invalid. If the interpreter is re-initialized again, the invalid pointer causes a segfault. The problem was first discovered by Trey Hunner in https://github.com/ethanhs/python-wasm/issues/69

python.js:219 Uncaught RuntimeError: null function or function signature mismatch
    at _PyUnicode_DecodeUnicodeEscapeInternal (unicodeobject.c:6493:25)
    at decode_unicode_with_escapes (string_parser.c:121:13)
    at _PyPegen_parsestr (string_parser.c:273:1)
    at strings_rule (action_helpers.c:901:20)
    at atom_rule (parser.c:14293:27)
    at primary_rule (parser.c:13916:17)
    at await_primary_rule (parser.c:13666:17)
    at factor_rule (parser.c:13542:29)
    at term_rule (parser.c:13330:17)
    at sum_rule (parser.c:13044:17)

I can reproduce the issue with pure C code:

$ gcc -Xlinker -export-dynamic -g -IInclude/ -I. -o ucnbug ucnbug.c libpython3.11.a -lm -ldl
$ gdb ucnbug
(gdb) run
0
9
Done

1

Program received signal SIGSEGV, Segmentation fault.
0x0000000000000000 in ?? ()
(gdb) bt
#0  0x0000000000000000 in ?? ()
#1  0x00000000005729a8 in _PyUnicode_DecodeUnicodeEscapeInternal (s=<optimized out>, s@entry=0x7fffea53b6d0 "\\N{digit nine}", size=<optimized out>, errors=errors@entry=0x0, 
    consumed=consumed@entry=0x0, first_invalid_escape=first_invalid_escape@entry=0x7fffffffc748) at Objects/unicodeobject.c:6490
#2  0x0000000000644fe3 in decode_unicode_with_escapes (parser=parser@entry=0x7fffea5e45d0, s=0x7fffea53b6d0 "\\N{digit nine}", s@entry=0x7fffea6af1d1 "\\N{digit nine}'", len=<optimized out>, 
    len@entry=14, t=t@entry=0x7fffea606910) at Parser/string_parser.c:118
#3  0x0000000000645675 in _PyPegen_parsestr (p=p@entry=0x7fffea5e45d0, bytesmode=bytesmode@entry=0x7fffffffc838, rawmode=rawmode@entry=0x7fffffffc83c, result=result@entry=0x7fffffffc848, 
    fstr=fstr@entry=0x7fffffffc850, fstrlen=fstrlen@entry=0x7fffffffc858, t=0x7fffea606910) at Parser/string_parser.c:269
#4  0x0000000000644163 in _PyPegen_concatenate_strings (p=p@entry=0x7fffea5e45d0, strings=strings@entry=0x94e310) at Parser/action_helpers.c:896
#5  0x00000000004791e6 in strings_rule (p=p@entry=0x7fffea5e45d0) at Parser/parser.c:15463
#6  0x000000000047c498 in atom_rule (p=p@entry=0x7fffea5e45d0) at Parser/parser.c:14274
#7  0x000000000047e159 in primary_raw (p=0x7fffea5e45d0) at Parser/parser.c:13908
#8  primary_rule (p=p@entry=0x7fffea5e45d0) at Parser/parser.c:13706