Forget what you think the sensors are saying. If you blow on a heatsink, can the cpu be colder than the air that is passing over the heatsink? Even if the cpu is off, it can't!
So either your water sensor is after your cpu and gpu, in which case it's useless, or your sensors are wrong. In fact, the only place it's worth having a water sensor is after all the heat outputs (radiators) and before all the inputs (blocks, pump). Then you know the lowest possible temperature for your cpu. BUT! The actual lowest temperature will be the CW rating of the block for your rated cpu PLUS the water temperature allowing for the flowrate.
e.g.
100W cpu
block with a cpu rating of 0.12 at your estimated flowrate
water temperature of 25C
Minimum possible cpu temperature is 12C over the water so 37C.
In this example, it is not possible for it to be lower than 37C. Period.
And in any rig, at any flow, with any block and any radiator, it is not possible for the cpu to be colder than the coolant.