When customer (or admin) deletes the stored CC from WHMCS, it will also delete the stripe token stored (and will in turn delete the Customer from Stripe as well through API call).
What do you see under the "logs" section in your stripe dashboard? There can be many reasons which could be causing this failure including incorrect card / cvv / exp month / exp yr / card declined / etc.
This is apparently an issue with your ccform. I did find couple of issues whereby the name and id tag were missing for the input boxes which caused similar errors as above.
This fixed the ticket view that was showing No tickets for Open, On Hold, etc. ticket statuses. However, the default view is still showing very old closed tickets. Any clues?
It is possible to create WHMCS cron with DotNetPanel as well. Select Website Availability cron from the Scheduled tasks option and enter full URL to cron.php file in URL to check field along with scheduling this task.