Is this a fake STM32F105? There is no parts listed with that many pins
STM32F105R8


  The STM32F105xx and STM32F107xx connectivity line family offers devices in three different package types: from 64 pins to 100 pins.


On the front page of the datasheet:


  LQFP100 14 × 14 m


The part is obviously available in a 100 pin package.

But hold on....

Now, this is where it gets interesting. You are indeed right, in that the STM32F105R8T6 should really be a 64-pin part, at least according to the datasheet.

In chapter 7 of the datasheet, table 62, you can find the part numbering scheme. According to that, R equals 64 pins while V equals 100 pins. This is consistent with the information on page 86 and 89, showing the exact marking layout for LQFP64 and LQFP100.

If I were you, I would take a picture of the chip and send to STMicroelectronics. Then update your question with their response, because this is rather interesting.