Write collision for multiple reads - PIC24 I2C
I can't find any CAP188 sensor datasheet online so I cannot verify that claim.

Some sensor will initiate measurement upon their call address, and they need some time to do so.

It's quite common that they will keep I2C line low during that time, until the measurement is ready to be read. Some chip can serialize the measurement during it's being measured, so the first read might work but not the second.

After your first address send, make a while(_RBx != 1); (rb being your I2C SDA or try as well SCL line) to wait the chip releases the line before the next write.

Other reasons can be:
- I2C speed is too fast for the chip.
- I2C delay between two write is too short.