Is it normal for an r-22 unit to rapidly drop from 70 to 40 psi on the low side at the very end of a cooling cycle?

Having trouble troubleshooting a Trane RAUC 30 ton condenser.

We've had problems with it for years, occasionally needing to reset it, but it recently started locking out every time after one cycle.

Pressures and temps seem within normal ranges while under full load: ~220 psi liquid, ~70 psi vapor. ~15 F subcooling. ~90 F ambient air temp.

The symptom in the title is the only thing I have to go on currently, but I'm not sure what it means (I'm just a maintenance guy teaching myself HVAC, but we've had several techs look at this unit with no luck).

On the circuit diagram it looks like there's a low pressure cutoff at 45 psi. It seems like dropping to 40 psi could trip that, then it rises back up to 50 or so from ambient heat and can be reset. I'm just not sure why it's dropping that low at that stage, or if I'm just making something of nothing and the problem is elsewhere.

Thanks for any help! We have another service tech coming in the next couple days, just looking for clues in the meantime.

submitted by /u/PM-me-in-100-years
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