Thanks to greven and jimla1965 for reporting an issue that seems to intermittently occur during the Rock-on repository update and processing on a Rockstor appliance, leading to timeout issues (the first instance reported was intermittent, the second instance reported was persistent).

https://forum.rockstor.com/t/another-take-on-unknown-internal-error-doing-a-post-to-api-rockons-update/7739/

and, more recently,

https://forum.rockstor.com/t/unknown-internal-error-doing-a-post-to-api-rockons-update-old-fix-gone/9035/

The current symptom can be observed in the Rockstor WebUI.

Unknown internal error doing a POST to /api/rockons/update

Further details can be gleaned from the two posts listed above.