The planetary system I am using: HyperPatch's RSS v2.0
I am using Mod: MarioG's Realistic Engine Overhaul v1.7
The First:
I am not sure if this is a bug in the game itself or a bug in this Mod. But it's really annoying.
After I started a launch, the game performed very normally without any issues for a long time. But as long as it takes enough time (probably a few days in the game), the engine will not be able to find the fuel tank. This happened suddenly and couldn't even be detected by me at first.
So I clicked on "SAVE&EXIT" and re entered, It's back to normal Thank goodness.
But this really affects my experience.
The Second:
I was about to let the re-entry module enter the atmosphere, so I slowed down the spacecraft. However, halfway through the deceleration, there was a problem and the engine suddenly couldn't find the fuel tank - That's the bug I just mentioned - so I clicked on "SAVE&EXIT" and re-entered.
When I re-entered, the speed of the spacecraft unexpectedly increased from 7700m/s to 7200m/s. This means that the entire planetary system operated for a while in the minute I exited, rather than pausing!
Another experience can also illustrate this point. I drove one of my spacecraft to a location and saved the location, preparing to launch the spacecraft here and practice docking. But when I exited and re-entered, I realized that the spaceship (not the one I was launching) had already arrived a hundred kilometers away.