I think the arguments are mixed up here:
https://github.com/rtklibexplorer/RTKLIB/blob/demo5/src/preceph.c#L83
ns=(int)str2num(buff,4,2);
The third line of the SP3-file contains the text: number of satellites
+__114 C06C07C08C09C10C11C12C13C14C16C19C20C21C22C23C24C25
It reads two characters starting from position 4, gets 14. But I must on the contrary to get 114.
Now he reads the first 14 entries for each epoch, and these turn out to be BeiDou. Accordingly, nothing further works without GPS.