To tell you the truth – I am not sure. I have run them up to about 50C for characterisation experiments and that was fine.

The electronic parts themselves all generally are rated to minimum 70 degrees, and in practice most of the sensitive ones (spectrometer etc) will usually be at a lower temperature than the liquid (since the internal air temperature is generally < liquid temperature). But, other aspects of the design might not tolerate this. I am not sure what the first thing to cause issues would be - perhaps the resistors on the heat plate at the bottom of the reactor, which are already substantially hotter than the liquid temperature, might melt their solder. In practice that is not a terribly difficult thing to fix, but it could happen. My feeling is probably 60 should be fine, but I wouldnt go much higher than that. Obviously test it on one reactor first and see how it goes before subjecting more of them to it...