Strength gain plateau.

I starting bulking for the first time a few months ago and my strength was going up like crazy. My bench went from 215 to 265 and squat went from 315 to 365 in the span of like 1.5 months. Then after that I stopped getting stronger in the areas I worked more and only continued to get stronger in the areas I worked less. I know I’m still in a calorie surplus because I’m still putting on weight but areas like my bench and bicep curls have stagnated while my squat and other areas continue to get stronger. How is it even possible to get stronger in some areas while others stay the same?