I have EE v2.5.3 and Freeform Pro 4.0.10 among other things.
When submitting forms with admin notify turned on I get a server timeout error. The form data still submits to the db and I still get a notification email but the server hangs and eventually times out instead of loading the return page.
If I turn on admin notify it works properly, but obviously no notification, which I very much need.