dbnSNP frequency anomalies Sometimes dbSNP reports very different allele frequencies for different large-scale genome projects e.g. between 1000 Genomes and GnomAD
rs11822440 1000Genomes A=0.4629    C=0.5371 GnomAD A=0.99997   T=0.00003
rs28531832 1000Genomes T=0.4379    C=0.5621 GnomAD T=0.99993   A=0.00007
rs78931618 1000Genomes A=0.7334    C=0.2666 GnomAD A=0.9999    T=0.0001
rs75716913 1000Genomes T=0.9006    C=0.0994 GnomAD T=0.99149   A=0.00851
Is this an issue with one or other of these projects data processing? Is something else going on here biologically or technically that might cause this?
I'll stick my neck out and simply state that allopatry alone would account for the pattern you are observing. Thus populations can exihibit variation in allelic profiles, particularly where Mendellian inheritance is operating (i.e. higher eukaryotes), singly due to geographic isolation.
This represents the Meyers view of population genetics and would account for variation within neutral theory, e.g. silent mutations. Obviously I'm guessing the populations were selected by geographic foci in generating the allelic frequencies.