I haven't seen any drift or bad flight characteristics that I know for sure were caused by this. Only that the GCS GPS map shows the wrong location. On the other hand, I can't rule it out as I haven't researched it. I also don't fly this way on purpose, so I don't do it often, and I can imagine some worse things if Home is a really long way away, like so far that the curvature of the earth is large.
The only bad things I imagine from 50km away from Home are that you are not flying where telemetry and the map says you are flying, and that if you use the GCS map to click up a waypoint flight then it is really bad because it does not fly where you think it should.
In my experience, most of my GPS drift has been caused by:
- not waiting long enough for GPS to fully "warm up"; up to 13 minutes for first flight of the day and much less for following flights
- GPS shadowing, like flying next to a tall building or in a canyon
- GPS signal reflections, like from a building or metal roof, or even cars
On first flight of the day, GPS downloads an almanac of satellite positions which can take up to 12 minutes after initial satellite signal. Most GPS's (but not the cheapest, smallest GPS's) have the equivalent of a battery that lasts about 6 hours and powers the storage for the almanac. Less than 6 hours between flights and it uses memory almanac, more than 6 hours and it has to download almanac again.
Once you get a good GPS lock, you can fly but if it finds an important satellite that it didn't see before, it will drift when it adds that satellite to it's list. If it has the almanac, it knows where all the satellites are it is less likely to add an important satellite during flight since it already added it from the almanac.