Kerberos Error APP_MODIFIED when using a CNAME DNS record
Solution 1:
The issue is the fact that the DNS entry is a CNAME record not an A record combined with fact that the SPNs are set up for the host name MyApp and not the machine name MachineB. The solution is to either change the DNS entry for MyApp to an A record that points directly to the IP address of MachineB or to add the SPNs HTTP/MachineB and HTTP/MachineB.Contoso.local (the old ones likely could be removed).