I2C hanging after 2 minutes
The small glitches you're seeing towards the ends of the last two bytes might be due to the master releasing the line so the slave can ACK. If that's the case, it's not crosstalk, it's just something that happens with I2C. It shouldn't be a problem.

I second the suggestion to try stiffer pull-ups and add a bypass capacitor to the LM75 if there's room for one. If this is a homemade circuit board, you should also measure the trace resistances to verify that the connection is good. You could also try reducing the bit rate. If that doesn't help, use your scope to look at the last transfer before the fail. A non-auto triggering mode will do this. Determine whether it was ACKed or NAKed or something else. Try to figure out how many transfers it takes to produce the fail. Is it the same number every time? Does polling more often than once per second make the system fail sooner?