Thank you so much for the feedback I will look into that bug asap!
Keep an eye out for future updates. I will definitely add more over time.
Update: both bugs have been fixed, check out the devlog!
So all % based upgrades are multiplicative, not additive.
For example:
If you had a crit chance of 10% and got a +20% upgrade you would now have 12% (multiplicative), not 30% (additive)
I hope that makes sense. You can always check your stats on the pause menu as well if you ever want to see how the numbers get affected after an upgrade.