brightness drops to 75% randomly

hello, i have replaced iPhones xs screen bought from ifixit (the OLED Packeg) replacement smooth and fine but i've noticed that time to time brightness off the display drops to around 75% (the top 25% won't do anything) and stays like that, seems pretty low and some time hard to see under sunny environments, reboot won't fix the issue but after sometime it fixes it self, is this a know issue? (BTW this 2nd screen replacement of the device first was done by Thirdparty and was working fine in these regales but had other issue which to me was a bad panel used by the shop even had bad fitting issues) this panel does not have such issue 3D touch is working fine too which wasn't working before. any idea what is causing this behaviour? BTW auto brightness works fine when this issue is not present.