It looks like you are reporting an old problem, which you had opened a few years back.
https://www.openstreetmap.org/changeset/95487626

Even though Magic Earth claims to use our data to create its navigation system, it is proprietary software and we have no idea how they built their algorithms.  Obviously, *they* are doing something wrong because OSM data allows a normal left turn here, all the routing engines I know can handle this perfectly, but Magic Earth cannot.

It makes no sense to us because doing the left turn from the main road is shorter and we see no objective reason why any sensible algorithm would ignore the fastest route (using the side road is longer; we know that some algorithms will favour longer roads if there is a possible gain but there isn’t any: same number of traffic sign, same surface, same maxspeed…).

As a last resort, I’ve just added a restriction to forbid the left turn from the side road—because that obviously looks dangerous.  This won’t affect our routing engines but maybe Magical Earth will now start ignoring this one and offer the other.  Make sure your app uses the latest map data and test again.