Custom configurations thrown out of whack

Nearly all my high powered custom configurations have had their tunings (specifically gearing and waste-gate limits) thrown out radically without any of the sliders showing that they've been moved or altered.
One of the configurations was an Ibishu Pessima (1st gen) that used the stock race gearing system and a tuned variable boost turbo, easily able to get up to 310 km/h. After the most recent update it can barely reach 170 because of the gearing.

I've tuned and retuned, dropped parts, changed gearings back and forward, and nothing seems to be fixing it. The stock race variant (with the same gears) does not have this problem and newly built configs seem to mainly avoid this problem.

I know it's simple enough to rebuild configs but for future updates and just curiosity, I'd like to know what's going on.

 

Still doesn't explain how multiple re-tunings and changing parts didn't do anything significant.