Hi...
I bet your M6 and your Nokton are 100% OK... Great equipment! Please let me guide you through a quick, effective test, although for your gear I guess you've been shooting for years... But this is really worth it.
Here's what's happening:
First and most important: the color. In all these shots you've used daylight film for scenes lacking direct sun. Just a bit of sun in part of the background of the one with children playing... You need to filter, because in photoshop the changes are different: less real. For the overcast and shadow scenes use the 81b or A2 warming filter, and for the tungsten ones, the cooling blue 80b or 80c. If you don't have them for your Nokton, consider buying them today, with the 8x ND (0,9) 3 stops Neutral Density (Gray) filter, to shoot your superb lens wide open on direct sun. I'll get back to these filters later...
Second, there's a bit of unsharpness because of handheld shooting, and also because of the narrow depth of field, but the lens seems OK and maybe your rangefinder has no issues.
Third, scanning a negative is a much more complicated thing than what people think... Not only because you don't really know how the original scene's positive should look like, but also because you don't really know how well exposed it is... Negatives require usually twice the light after an incident metering, but I recommend you not to use negative, just for this serious plan to get wonderful photographs today! I bet if you do it, you'll be very happy!
Buy one single roll of slide film. Any ISO 100. Buy the three filters (so very important...) The filters should be B+W, Nikon or Hoya.
The scenes and subjects are totally secondary, as composition, because the tonal results will be beautiful. The goal is shooting (on a sunny day) three scenes with different light in the same roll: one under direct sun, one in the shadows, and one in tungsten light, all of them with a tripod.
You'll test here both color and focus, so you should do the same scene wide open, and by f/5.6. It's easy and fast, and I guess writing all this takes more time...
I don't know if your M6 is TTL, but anyway, with a simple bracketing you'll get it perfect or near perfect. Don't know if you got an incident meter: again, anyway, you'll do well.
3 shots (-1, N, +1) under sunlight wide open with the ND filter (considering the light the filter absorbs), and 3 shots of the same scene by f/5.6 without the filter.
3 shots in the shadows with the warming filter wide open (absorbs near ½ stop), and 3 more with the same filter by f/5.6.
3 shots -maybe home- in tungsten with the blue filter (absorbs 1 or 1 ½ stops) wide open, and 3 more with the same filter by f/5.6
That's THE ONLY WAY to see how your gear is working...
Feel free to send me a PM for more details or ANY question...
Cheers,
Juan