Legendary Tuner kinda softlocked my car?

So I decided to test renting out the power unit upgrade from the Legendary Tuner. Said it only lasts for a day but after finishing the day and earning enough to get power level 2, I couldnt buy it, much less equip it. Or switch it back to genuine part.

Here's the rundown, with the rented upgrade, my car have 207 ps rn. The stock version is 200. After the rental period, it still stayed at 207 ps and I couldn't buy any upgrade for the power unit.

I decided to test it out again, this time, my ps went from 207 to 208. Did some races and as the day ended, it went back to 207 so wtf. Safe to say, my car cant be upgraded any further now thanks to that.

The car in question is the GT86. Maybe the Legendary Tuner is bugged? Like the original stats of my car didn't go back after finishing the day and since the game was saved, there was really no going back from there.