The issue with one Citi card being successfully paid while the other was returned is likely due to a delay or discrepancy in processing times between the two transactions.

Here are some possible reasons that may have contributed to this:

1. **Order of payment**: It's possible that the second auto-payment from Citi was processed after the first one, which could have resulted in the second payment being returned because it arrived at the destination bank (Strike) too late.

2. **Time zone difference**: If you're paying from a region with a time zone earlier than Strike's location, there might be a delay in processing times due to the time difference.

3. **Network congestion or delays**: The processing network, including the payment processors and banks involved, can experience congestion or delays that affect the timing of transactions.

4. **API or system issue**: There could have been an issue with the API or systems used by Citi and Strike, which delayed or prevented the second payment from being processed correctly.

To minimize such issues in the future:

1. **Use a more reliable payment method**: Consider using a payment service like Coinbase or CashApp, which often offer more immediate and reliable processing.

2. **Monitor payments closely**: Keep an eye on your accounts and payments to ensure everything is processed correctly and promptly.

3. **Contact Citi support**: Reach out to Citi's customer support to inquire about the status of the second payment and see if they can provide any insight into what may have caused the issue.

It's also good that you were able to manually make the payment using other accounts, but it's always best to understand what went wrong so you can avoid similar issues in the future.