1. There is a common bug in Update 20.1.3 in Universe Sandbox 2 which causes planets to turn black when receiving collisions and also when changing their size. All this time and the bug has not yet been fixed.
2. Another common, recurring bug is when loading a saved simulation, and habitable planets stay frozen when temperatures are above 0 degrees Celsius, even why frying rocky planets to their thousands of degrees Celsius.
3. There is also a very common mass loss bug on cold and frozen planets which should not appear. The mass loss should only appear on planets when they are vaporized by the star, or even when a supernova goes off at a safe, but close distance. Planets which are less than 2500 KM in radius unexpectedly lose mass and mass loss is also triggered by changing the composition of planets, gas giants and stars, such as adding or removing water or silicates.
4. When creating a large rocky planet and colliding a gas giant that is smaller in radius, the larger rocky planet disappears. This is also a known bug and it must also be fixed.
Those are some of the most occurring bugs that appear all the time in Universe Sandbox 2. Those bugs causes the most problems in Universe Sandbox 2. If you discover more bugs and technical glitches, please report them in this forum here.
Universe Sandbox 2 is currently on Update 20.6. So far there has not been any fixes for those bugs I have mentioned above. I hope that Update 21 will solve the problem with those bugs and fix them all once it for all.