Can't save resources/elements - content too long?

I'm having trouble saving some resources and elements on a particular website - I've not had the issue before. For what it's worth this problem started on Revo 2.2.13 and has continued to 2.2.14.

The basic problem is that when I save a resource that seems to contain more than a small amount of content (approx 100-130 characters), the save fails and the page hangs. Developer Tools shows a POST 404 error when retrieving http://www.domainname.com/connectors/resource/index.php, though the file is clearly there and, up until recently, saving resources hasn't been a problem. In fact, saving works fine when the content is small enough. There is no other significant data associated with the resource; even when using the default "blank" template, which has no TVs associated with it, the save fails.

I thought it might have to do with the post_max_size setting in PHP - I've had the host change this from 8mb to 32mb with no success. Apparently mod_security is in play, and the host has made some corrections regarding this, but I'm not sure what, and the issue still exists. Regardless, the MODx installation flagged no issues with mod_security or suhosin, so I'm not sure if there's actually an issue there. There are no significant error messages to be seen in any of the logs, which seems odd to me, but may be indicative of the POST data not reaching it's intended target, and therefore no scripts being initiated and no errors being created.

I'm in the blind on this - if anyone has any ideas, or has come across this before and knows a solution, I'd love to hear it please.

That does sound like mod_security or suhosin. It can have its own maximun POST size that has nothing to do with PHP. Or sometimes the most unexpected word can trigger it. Can the host turn it off for you completely, at least temporarily, so you can see it that is, in fact, the problem?