Does anyone know what could be causing this sensor problem- detection only when unpowered

We are currently using temperature sensor and Bar100 pressure sensor. There have been problems with them not being discoverable/communicable over I2C that I have been troubleshooting the past few months. (I had a previous post about this about a month ago). Progress has been made, and it seems like the hardware on the Raspberry Pi may have been part of the problem, as was previously suggested by a BR team member. However, it does not explain everything. Recently a phase has been entered where the sensors will only show up under an i2cdetect scan if and only if the voltage supply lead is NOT connected. I can have the ground, data and clock wires connected, and the sensor addresses will show in the scan. But, as soon as the voltage supply/hot/red wire is connected, the sensors will disappear.

I have double-checked this many times. The voltage supply pin (on the raspberry Pi) is the correct voltage. Everything is plugged in correctly. I measured with a multimeter and the voltage level seems to be correct coming out of the Pi and onto the breadboard. I and the rest of the team are at a loss to explain this behavior. Does this indicate an internal hardware problem with the sensors?

Well, I’m pretty confused as well… The sensors are getting identified with no power? could there be enough power in the other lines to power at least the i2c portion of the chips?
have you tried seeing the signals with a scope, or maybe talking to the devices using a different system, like an Arduino?

As far as I am able to test, the bus is outputting the correct signals. I think we do have an arduino, so I might try to test with that next semester.