I’ll speculate on your first question but I’m pretty confident in my hypothesis for your second question:
In the absence of hydraulic pressure, both elevators were drooping, but to different degrees, right? I’d guess that the elevator that drooped less had a little more friction in its bearings and/or hydraulic actuator than the droopier elevator did. That may be the case even if one elevator was angled up and the other drooped. Either way, I’d bet the higher-angled elevator had enough stiction not to move once the hydraulic pressure bled down.
Regarding the stepwise rise in cabin pressure, I’d bet you’re seeing the effects of pulse-width modulation (PWM). Cabin pressurization systems use actively-controlled valves, and it’s fairly tricky to control a valve such that it’s held open a certain amount, thereby allowing a particular flow rate.
Flow rate depends on valve opening position, but also air pressure, temperature and flow direction. Also, solenoid valves are likely candidates for this sort of thing, and they’re inherently bad at holding a partially-open position. They’re typically either open or closed. By opening a valve for two seconds and then closing it for eight, you get about 20% of the max flow rate without needing a more-expensive, more-complicated valve that can be held partly open and the attendant flow controller to measure the flow and adjust the valve to hold the desired flow rate.
So, most likely, the environmental control system is opening the relevant valve fully for a moment and then closing it for ten seconds. The finite outflow rate produces the curve you see at the edge of the plot’s steps, but these small, short steps approximate a slow, steady re-pressurization rate that’s friendly to human eardrums.
P.S. From your other posts, Machine Elf, I’m guessing you may already know about proportional valves and PWM. I’m not trying to patronize you; I explained in some detail for anyone without that background.