My apologies for the lack of info and follow up on this. After years in development and support I know you needed more info the I could give you at the time to define the problem. I just didn't have the time to put it all together.
Whatever happened resulted in corruption such that even though all group information can be displayed (number of members, discussion count, picture count, etc.), but clicking on a group to actually enter it results in a 404. It had been working but I have no idea what I did to cause the corruption.
I did try upgrading to 4.9.5 but that didn't fix the problem. I don't think upgrading can fix the corruption, we'd probably have look through the database to find what was wrong.
At this point I've started over. If the issue appears again I'll open a new thread. We can close this one.