BLTouch calibrated, nozzle still dives into the bed
This answer is intended to be a generic answer for Z-offset determination. The question is not clear on how the Z-offset has been determined. It appears as if this distance is measured, while in reality this cannot be measured.

A touch (or a inductive or capacitive) probe uses a trigger point to determine the distance of the probe trigger point to the bed print surface. Correct installation is trivial, as is the determination of the nozzle to trigger point definition. For a touch sensor, the probing element is either stowed, fully deployed, or pushed in during leveling up to the point that the trigger point is reached and the probe stowes the rest of the pin, see figure:



The M851 Zxx.xx offset is determined by lowering the nozzle beyond the  trigger point until the nozzle hits a paper sheet. If the stowed position to nozzle distance is used, the distance is too large and the nozzle will dive into the bed on printing.