I2C communication problem with two slaves (atlas scientific) and one Nano (official)
Two ideas.

1: Count your grounds. If you count more than 1 you have a problem. Your system should have a single ground, so ANY connection on every component labeled GND should be connected to ground.

The reason multiple grounds are a problem is that your signals (other than differential signals) are measured relative to ground, so if two components have different ideas of what "ground" is they start to disagree about what constitutes a 1 and a 0.

2: Scope your power supply. Check that your 5V supply is still providing 5V. It's possible (although unlikely) that the L7805ACV can't supply enough current and your system is browning out. If possible have a look with an oscilloscope to check for noise on the 5V supply.

Your boards should already have decoupling capacators, but adding another won't hurt, so also try adding a 0.1uf cap between 5V and GND to eliminate any noise.