They had this message on their app:

> Please note: Zelle transactions made between January 14 and January 17 may be delayed in occurring and posting to accounts as requested. Transfers will be completed and will appear in your account activity and balances as soon as possible. We apologize for any delay or inconvenience.

Given the date range provided and the recent MLK holiday on Monday, I’d wager that there was an issue with BofA’s Zelle system not counting MLK as a holiday. If the batch processing for BofA didn’t run Monday, but Zelle wasn’t aware of the holiday for whatever reason, then Zelle would try to reverse all the transactions because it had no data from BofA’s normal batch processing.

That’s just a guess but I think it makes a lot of sense given the date range for the issues and the time at which people started noticing their account balance being wrong.