Hi,
This is a big leap, and there have been quite a few versions in-between. I’m not sure, but maybe you can open and save the config using the latest version of the 3.x branch, and then try again. If this does not work, maybe try the first 4.0 version as a stepping stone and them try the latest version again.
If you have any F12 errors for me, I might be able to fix it.
Alexander