This is probably one of the areas most in need of a better, more reliable solution. Its very tenuous much of the time, with inadequate error messages or other debugging info.
Of all the things i have dealt with, I would say register is just about number one in the list of things the LLM or community should improve and/or simplify.
It takes forever, first of all, making all the pages and so forth (could be a package to do all of that automatically) and then if it doesn't work its hard to know why. Then when it finally *seems* to work you are just looking at it like a wobbly jenga tower, ready to come crashing down at a moment's notice.
And when it does come crashing down, you won't be informed right away because there is no verification or auditing, and who knows when a kind soul will tell you there is a problem :-(
And as we all know, if you are asking your new members to deal with a bunch of bs just to get into your forum, you are in serious trouble already.
I know the LLC has a lot on its plate, but this is definitely at the top of my to-do list for them :-D
You might look at the Subscribe extra, which wraps the register snippet (among other things) and does most of the work for you, though you need to style the pages to match your site.
Ok I will have a look, I never tried it out before.