What setting is your meter set to? There's multiple voltage ranges: 10, 50, 150, and 300
Those panels open circuit voltage listed as 21 volts. None of the ranges in the meter would read 21 volts, but it could be 32, 12, or 2.2 not just 60 volts.
But, if you're measuring 60 volts, is that battery voltage? If you have a 48 volt battery that would be overcharged.