>> 
>> How should I go about debugging this?
> 
> Run the offending command under a debugger, and try to find out which
> code in loadup.el causes this.  On macOS, this is a bit tough, since
> GDB doesn't work,so you cannot easily examine Lisp data using the
> commands in src/.gdbinit.
> 
> You could also try bisecting to find the offending commit.

Thanks. I figured it out.

Now that the tree-sitter integration is mostly done, anyone would like to look at the patch? 

Yuan