NorioDS Thanks for your comments.
Regarding #1, this extension wasn't made to manage so many distinct redirect rules. Not only does the setting size is limiting, I also suspect you might hit poor performance because I check every single rule one after another. I'd be interested to know how it performs.
If your redirects are "hard-coded", I suggest you use Apache or Nginx redirect rules instead.
This extension makes use of "rules" to redirect. It's best used with templates and match rules to redirect. If you're redirecting from an old forum to new discussions, it would be great if you could use a single rule to catch them and redirect. If you have to match from old slugs to new discussion ids, I suggest you create/adapt an extension like the MigrateToFlarum VBulletin redirect extension, which does look up inside the discussions table. Of course it's entirely based on ids (which can be offset). For slug-based lookup you'd have to add a column to the discussions table with the old slug for the extension to use.
Regarding #2 it looks like two issues:
The text that ends up as ____ is probably because of Flarum slug rules. I can't do anything about that. You could use extensions to change the way your Flarum creates slugs.
If you are indeed breaking the regex and either receive a 500 error or the regex doesn't match, please open an issue on GitHub with the details of the rule you used and the url causing errors. If you check the source code I am indeed using
preg_quote() to escape the text, but it's quite possible there's some issues in there ?