Chip lottery (chips from batches have slight variance) means that no two cards are identical twins.
Now as for them selecting different algorithms… I have four msi 1660 supers. Sometimes 3 do dagger and 1 kawpow, sometimes 4-0, and sometimes 0-4. They are all tuned the exact same. But they can sometimes run different temps which will affect their efficiencies.
Also, nicehash selects which algo a miner based on what pays best, but you can curtail or even stop that by dictating in the benchmark menu which miners and algorithms are enabled. I have my 6 card rig restricted to Phoenix-dagger, nbminer-kawpow, and gcuda-kawpow. I ket them switch back and forth between the three as nice hash sees fit.
I would recommend reviewing your benchmarks, temps, and ambient temperatures and see if maybe there might be a root case in one of those areas imho
Also if you’ve lost a benchmark it could have been because a miner updated and it must be benched with the newer version