Unfortunately, things are worse than expected. The error message above is an indication that your backups have likely been corrupted.
Try to run the Verify Backups check again. If it continues to fail, you will need to erase the Time Capsule disk and start over again with a new backup.
Unfortunately, no guarantees at this point because this will still not solve the issue if the disk itself is beginning to fail, which is a real possibility at this point.
Your Time Capsule disk is at least 7 years old and as much as 13 depending on then the Time Capsule was originally placed into service, so even if we can get the Time Capsule backups working again, my advice would be to begin thinking about a new backup plan that would not include the Time Capsule.
As you probably already know, the next Mac operating system will not support backups to a Time Capsule.