It has nothing to do with processing power or graphics. It is only about memory. Let me explain it with a metaphor.

Memories in a device are like rough-work papers. The processor and the graphical chips are like the calculating speed of the student.

In the classroom, there are many students. The teacher has, for example, 100 pieces of rough-work papers. The rule is: You may ask for a rough-work paper but you have to return it after your calculations.

Usually, you will work on the paper until you have written it full. And when you go on to work, you know something will no longer be useful for you, you will put a cross out there to tell yourself this is no longer useful.

When the papers are full, you will search for crosses, empty those space and use it to do newer calculations. You will only request more papers from the teacher if all the papers are used up and no crosses are found.

When RR3 loads, it requests for, for example 70 pieces of papers. It uses more papers while loading a car's model, updating the TSM, updating the images in the main menu, loading liveries etc. For some reasons, after loading a car's model and when the car's model is no longer needed (like maybe you just want to view the Silvia and then you decided to switch to Endurance Kings, the Silvia's model is no longer needed), RR3 forgets to put a cross at the Silvia's model. For some other instances, he might have dropped one or two onto the floor without realizing it as well.

When you go on to play the game, as RR3 is not reusing its own papers, it quickly runs out of papers and ask the teacher for more. This causes low FPS.

When the teacher allows RR3 to take more papers without stopping him, eventually, all the papers in the classroom run out. This crashes RR3. But he only returns some papers to the teacher. Some papers just fall onto the floor without being realized.

When you restart RR3, it still requests 50 new papers from the teacher. It eventually runs out and it crashes again. Thus, more papers are scattered onto the floor without being realized. That is why restarting the game may fix the crash but it eventually worsens.

If you restart your device, all the papers are returned to the teacher including those on the floor. When RR3 starts again, the papers will all be clean for RR3, that is why restarting the device works sometimes. But RR3 still has some remaining memories. These memories take the form of log files or config files. These files are saved in the harddrive and affacts the calculating methods he uses.

Uninstalling and reinstalling RR3 will erase these log and config files. RR3 will learn how to calculate from the beginning. All the wrong methods will be erased. This is why reinstalling the game may work for some cases.

But still, RR3 is coded poorly and he always forgets to cross out things he no longer uses. I hope the metaphor is comprehensive to you all.

Edit: Fixed a wrong concept.