SOLVED:
Updated my certificate using the following steps

1. Download the following file https://curl.haxx.se/ca/cacert.pem
2. Put it somewhere on the NAS.
3. SSH into the NAS
4. Run the following command:
   /share/CACHEDEV1_DATA/.qpkg/Qmono/bin/cert-sync /[LOCATION of THE cacert.pem FILE]/cacert.pem
5. Restart the Jackett application.

Seems to work just fine now

Jackett version: 0.8.402.0
Mono version (if not using Windows): QMono 4.8.1.0 running on QNAP NAS fw 4.3.4

This just started happening today.. the relevant logs leading up until the problem are:

Nov 10, 2017 01:45:36 PM | Error | {0} -- | -- | --
Nov 10, 2017 01:45:35 PM | Error | On attempt 3 checking for results from RARBG: An error occurred while sending the request
Nov 10, 2017 01:45:33 PM | Error | On attempt 2 checking for results from RARBG: An error occurred while sending the request
Nov 10, 2017 01:45:32 PM | Error | On attempt 1 checking for results from RARBG: An error occurred while sending the request
Nov 10, 2017 01:45:31 PM | Error | {0}
Nov 10, 2017 01:42:24 PM | Info | Starting web server at http://*:9117/
Nov 10, 2017 01:42:24 PM | Info | Deleting JackettUpdate temp files from /tmp/JackettUpdate-v0.8.402-636459181348532810
Nov 10, 2017 01:42:24 PM | Info | HttpWebClient: Disabling certificate validation
Nov 10, 2017 01:42:24 PM | Info | Adding aggregate indexer