Oracle DBMS_DEBUG.GET_VALUE can't get variable values when debugging large packages

I try to debug some function in PL\SQL. When I debug large package (package body contains 21666 lines of code), I can't see variable values, I always get (Not a variable).

I added debug information.

When debuging smaller packages this problem don't ocures.

This is part of PL\SQL Developer debug log:

begin
  handle.owner := :package_owner;
  handle.name  := :package_name;

  if :inbody = 1 then
     handle.namespace := sys.dbms_debug.namespace_pkg_body;
  else
     handle.namespace := sys.dbms_debug.namespace_pkgspec_or_toplevel;
  end if;  
  
  :result := sys.dbms_debug.get_value(variable_name => :variable_name,
                                      handle => handle,