Power Meters / Powermeters (SRM, Powertap, Quarq, Ergomo, Vector, Stages, power2max, P2M, 4iii, InPower, Cinch)

Have you lost weight?

Any advise?

If you want advice, I advise you to take English lessons.

I lost >30w between September and December and am only just now beginning to see a small uptick.

This has been almost perfectly associated with training effort. My advice is to train harder.

Assuming you're basing this off a single test?
In which case... when rested, test again. Was the test protocol the same?
Mind you, detraining hits after a week or so, so it's possible you've just been slack.