The problem is that URL’s changed entirely. So for instance, this:
https://greaterthangames.com/forum/topic/a-guide-to-serpent-slumbering-beneath-the-island-10888
Became this:
https://forums.greaterthangames.com/t/a-guide-to-serpent-slumbering-beneath-the-island/17388
Which, in some cases, can be replaced easily, because https://forums.greaterthangames.com/t/a-guide-to-serpent-slumbering-beneath-the-island/ (without the ID number) works just fine. I’m not sure that will work for all links, though.
If no better solution comes up, you could do a find-replace with a few lines of code, depending on the backend.