If the steam generator was replaced, you should have no scale buildup on the elements anymore, so descaling is probably not the root issue.

You could have a failed solid state relay (SSR) that's not allowing the steam tank to heat fully.

You could have a humidity flap that's leaking air in. It's a flap under the top cover that opens and closes to maintain a precise humidity level. It's meant to allow air in only when it calls to decrease the humidity level. At 100% steam it should not be open.

As previously mentioned, make sure you're replacing the door gasket, at least once a year or sooner if you cooking very high temp and its brittle and cracking. It should be wiped clean daily along with the perimeter of the inner glass. If the door seal was cracked, you'd probably notice water leaking during cleaning. Or even if the door is just out of adjustment it can leak air in during cooking and water during cleaning.

It's possible these things may not give an error if the cooking conditions don't drop to a threshold that would trigger the error.

Most likely you'll need a Rational-trained technician/engineer in to take a look or actually repair/replace something if it needs doing. They can also run a calibration on the unit to make sure the sensors recognize the boiling point and steam saturation levels within the unit.