I've been using the FMS-OnlyModifiedSince header, and everything seemed to be going well.

As of this morning, however, it doesn't appear to be working correctly.
The first time I hit a page (e.g. https://frc-api.firstinspires.org/v2.0/2019/avatars?page=12) and send an FMS-
OnlyModifiedSince header OR a If-Modified-Since header, I get a completely empty body and I see that there's a Cache 
Control header with the value "proxy-revalidate".

If I then hit the page without either of the last modified headers, I get the response I expect, and subsequent calls 
with the headers work correctly for that page of data.

However, even after doing that, the headers don't appear to be working correctly. I have tried both headers with a value
 of "Fri, 22 Feb 2019 14:56:20 GMT", and I see in the response a Last-Modified header with value "Fri, 22 Feb 2019 14:56
:19 GMT". However, the body is the exact same as if I had not sent the headers at all (i.e. all values are returned).