The recurring donations failure scan yielded several GC transactions that show as recurring in Civi, but do not show as recurring at the GC portal: transaction IDs are 4699088506, 630660817, and 6880374848.
There are also several possibly-related transactions that do appear as recurring donations at GC, but have not processed again yet, though this may be due to normal variability, as they are two days overdue: 3005420957, 2185631244, and 9264844762.