Inconsistent readings using Pressure / Altitude sensor (MPL3115A2)
... any suggestions on accurately measuring the elevator height would also
be appreciated.

As per my comment, another option is to monitor a mark (or several) on the elevator cable drum with a pair of sensors and make an incremental rotary encoder. This is very simple and reliable.



simulate this circuit &ndash; Schematic created using CircuitLab
Figure 1. 2-bit rotary encoder waveforms.
The program logic is very simple.

Track the current state of 'A'. If the state changes to 'high' then:
Look at input 'B'. If 'B' is low then count up. If 'B' is high then count down.

You'll probably need to debounce the inputs to prevent spurious triggering.

Figure 2. Elevator encoder. A and B photo-sensors looking at reflective tape or high-contrast markings on winding drum.