The speed is sometimes zero for long periods (even though the fix is achieved, and the position is correct). In this case the altitude is also bad, it’s “frozen” (the same incorrect value is kept for long time).
However, with my application this is not always the case, it just happens from time-to-time, but for long periods (up to half on hour).
I have the same configuration, but I’m using GCC.
This is surely not a conversion problem, as the speed value is OK when it is given…