Expressions don’t report to dataMine2. Although the sensor is present it does not report any useable data for dataMine2, which is not catastrophic but might be noted as a future improvement.
The expression-value in dataMine2 is dead to zero.
Well, if the ReactorSensor’s state variables are changing, it’s doing what it needs to do. I can’t imagine what, if anything, dataMine may need beyond that. I don’t use dataMine(2), so I can’t offer much more help there, except to suggest that you might be sure you’ve reloaded Luup, as I know a lot of plugins only set watches on variables at startup time, so it may just need to be tickled to get going.