There are numerous "focus shift" grumblings with fast 35mm focal length rangefinder lenses, but I really think that these types of lenses require the users to know how to use them -- and manufacturers have not generally been good throughout history about explaining how to use these lenses. When lenses like the V1 35/2 Summicron and the 35/1.8 W-Nikkor came out, they represented some of the most (or "the most") advanced 35mm RF lenses made to that point. They were extraordinarily expensive. Leica and Nikon already had very competent, slightly slower 35s in the form of the Summaron 35/2.8 and W-Nikkor 35/2.5. The fast 35s shifted, the slower 35s generally did not.
Today, many people who are new or relatively new to RF photography get initially flabbergasted by the fact that their Summiluxes and pre-ASPH Summicrons "shift." If you are coming from a film or digital SLR, this comes as a shock as the vast majority of modern SLR lenses have no noticeable shift (and your mirrorless camera can now automatically compensate for any shift in the newest lenses anyway). While many people did not notice this too much during the film era, digital mirrorless is unforgiving for any lack of precise focus on the sensor plane. So yes, your V1-V4 Summicrons and older Summiluxes will look out of focus when correctly focused with the rangefinder at f/5.6 on digital (and also on film) because that is how the lens behaves. What is really great about digital is that with liveview, you can actually focus absolutely spot on at f/4-8 with fast 35s, whereas during the film era, you may have had to guess or manually compensate in some way. I do not really understand why one would use a digital M without liveview -- that's the whole point! 100% accurate focus every single time without worrying about the primitive native focusing system.
Although I have not handled any of these replicas, copying the original design will generally copy the original focus shift (like the UC-Hexanon's copy of the W-Nikkor copied almost precisely the shift of the original lens). The V1 35/2 Summicron was designed for pros who "needed" f/2 over f/2.8. The technology required to create an f/2 lens that focused accurately at that aperture required compromises. One of those compromises was that if accurate on the rangefinder somewhere at f/2-f/2.4-f/2.8, it was not going to be accurate at mid apertures. You would either use the Summicron wide open, and if you need to capture a larger scene, at f/8-11. I do not think that older Summicrons and Summiluxes were considered or are to be considered "general purpose" 35mm lenses. That is what the Summaron was for.
