I usually get unproductive when i do a run at a leisurely pace. the FB algorithms don't seem to think recovery runs or what my training plans call general aerobic runs have any value.
according to Fb algorithms i should just do intervals all the time. according to them the aerobic training effect of a 5x1000m session is greater than that of a 34km run...
When I have run hilly, high-elevation gain runs, my Fenix 6 has labeled them as “unproductive”. My take is that it mis-judges from my expectedly lower pace (5:30mins/km in 250m uphill in a 10k run, compared to my 5:05mins/km on my normal totally flat 10k run) that my VO2max has deteriorated, which is most certainly not the case.
I therefore suggest you recalibrate your training to include a flat, fast run of the same length which you will perform at your best pace, to give the software a chance to measure your performance unobstructed by the uphills.
Having said that, I find it very disappointing that Garmin doesn’t take into account the productive VO2max training that running uphills gives.