Updated to 18.10 then factory reset the watch and removed the bluetooth pairing profile (from my smartphone's settings & garmin connect device).
Then set the instinct solar up as new device and calibrated the elevation at a known location using DEMS and have found it to maintain consistent & accurate elevations so far. Even with driving where I change 400 ft of elevation within a few minutes. Battery performance has also been stable. The only thing I find off is sleep tracking but my pulse ox feature while sleeping is disabled which may have an affect (IDK).
Is everyone else having a similar positive experience?