Yep, this also break IPython command completions when users press tab in some places in multiline code.

88f4ec88e282bf861f0af2d237e9fe28fbc8deac is the first offending commit for me in the 3.9 branch:

    [3.9] bpo-45494: Fix parser crash when reporting errors involving invalid continuation characters (GH-28993) (#29071)

    There are two errors that this commit fixes:

    * The parser was not correctly computing the offset and the string
      source for E_LINECONT errors due to the incorrect usage of strtok().
    * The parser was not correctly unwinding the call stack when a tokenizer
      exception happened in rules involving optionals ('?', [...]) as we
      always make them return valid results by using the comma operator. We
      need to check first if we don't have an error before continuing..
    (cherry picked from commit a106343f632a99c8ebb0136fa140cf189b4a6a57)

    Co-authored-by: Pablo Galindo Salgado <Pablogsal@gmail.com>

    NOTE: unlike the cherry-picked original, this commit points at a crazy location
    due to a bug in the tokenizer that required a big refactor in 3.10 to fix.
    We are leaving as-is for 3.9.