I did, I removed it all down to just the IPS rules and it still resulted in the same issue. Also worth adding, the htaccess file that was working wasn't changed for years. So something changed, either at the host level or at the IPS level. I can't tell which because it's a single server with 3 instances of IPS runnings where two work and one doesn't. The FURL rewrites seem to work fine, but the API menu in the ACP keeps prompting me to install the htaccess file in the api directory (which I did) but hitting Continue does nothing but reload the initial page.