Recently I upgraded my emacs 25.3 to Emacs 26.1 for window. In the emacs 25.3, it installed the org version 8.2.10 by default, and the newer emacs 26.1 builds with org version 9.1.9.
When I want to open a org document(19M) with org version 9.1.9. It seems to take long time for opening this document, the emacs seem to be paused. So I change the emacs 26.1 to use org 8.2.10, simply replace /emacs-26.1-x86_64/share/emacs/26.1/lisp/org with the files of org 8.2.10. The result is good, It open the same file smoothly. So I guess whether If there are some issues in org 9.1.9, they need much more time to open this document? By the way, The file that cannot be opened contain a large number of radio targets, which may be the reason that it is slow to open
The above testing document is so heavy, that the mailing list of orgmode can't to load, So if you want to verify the situation I met, please send the mail to me, I will send it to you directly. Thanks!