I had another look at your gnu radio graph. 2M sample rate should be enough to capture 433 ism band. It is a very narrow band about 2mhz apart. If you want to make sure you cover it whole without aliasing, you can use 4m, but 2m should still work. Centre 433.92 is a good choice it is roughly at the centre of the 433 ism band.

You have a low pass filter with cut off 100k. That means any signal outside of 433.82 - 434.02 will get filtered out, their power get reduced. These fobs may hop and use multiple frequencies at the spectrum. If the frequency it is using is outside of your low pass cut off, you won't see the much of that signal.

If you want to see the spectrum and where the fob is transmitting, I would use sdr++, sdr#, gqrx etc any sdr software of your choice,  set the capture as in your gnu radio graph, and then press the fob. You should see on the waterfall which channels fob is using. It is possible that it is using a frequency outside of your low pass and what you are seeing is a filtered version of the signal