Why does the DB ticket machine show too little credit or a Geldkarte balance of 0€, even though there is sufficient credit on the GeldKarte chip?

When I recently wanted to buy a ticket and conveniently paid for it with my credit balance via the GeldKarte function on my Sparkasse card, the machine indicated that my credit balance was insufficient, and the account balance was completely incorrect. I've encountered this problem with at least three different DB ticket machines. Has anyone…