It appears that background simulation is greatly accelerated on a ship that has asteroid harvesters in use.
In the attached file, see "Kerbin Skybase 2", which is harvesting an asteroid. If you switch to another ship, let some time pass (e.g. a few seconds at 50x), then switch back to KS2, several hours or days will appear to have passed - e.g. greenhouse is days closer to done, oxygen/nitrogen consumed, CO2/waste produced, kerbonauts are more irradiated.
If you turn off the drills and repeat this, the background simulation proceeds normally.
This is tested on KSP 1.3 with only the mods Kerbalism 1.2.9 and Kerbal Engineer Redux 1.1.3.0 (couldn't remove this, KS2 ship has a part from it and doesn't load without it)
Related: I installed a mod called Exception Detector, and it reports many many exceptions in module KERBALISM.Background.ProcessAsteroidDrill in these circumstances.
It appears that background simulation is greatly accelerated on a ship that has asteroid harvesters in use.
In the attached file, see "Kerbin Skybase 2", which is harvesting an asteroid. If you switch to another ship, let some time pass (e.g. a few seconds at 50x), then switch back to KS2, several hours or days will appear to have passed - e.g. greenhouse is days closer to done, oxygen/nitrogen consumed, CO2/waste produced, kerbonauts are more irradiated.
If you turn off the drills and repeat this, the background simulation proceeds normally.
This is tested on KSP 1.3 with only the mods Kerbalism 1.2.9 and Kerbal Engineer Redux 1.1.3.0 (couldn't remove this, KS2 ship has a part from it and doesn't load without it)