So what happened Monday morning, anyway?

SEPTA is pointing to a high level of usage all at once as a potential cause of its Key card glitch that complicated the early-morning commute earlier this week, prompting the transportation agency to waive fees for those affected as issues persisted.

Key holders saw problems reloading cards for about four hours, starting just before 7 a.m. While SEPTA is still reviewing issues with Conduent, the primary Key contractor, an “initial analysis” showed “it is possible that the issues were related to an unusually high level of attempted transactions within a short period of time,” SEPTA spokesperson Andrew Busch said in an email.

The loss in passenger revenue is estimated to be less than $50,000, though an exact figure is still being determined.

“SEPTA and Conduent have been working collaboratively to identify and address the issues that occurred during the morning commute on Monday, Dec. 2,” he said. “Conduent has been adding capacity to meet the increasing needs of SEPTA customers to ensure efficient transactional performance. In response to the difficulties experienced by our customers on Monday, we are doing a full examination of systems and processes to ensure transactions are quick and accurate.”

So what went wrong? Not only was Monday the first weekday of the month, but it was back to reality for travelers returning from the Thanksgiving weekend. Many looked to buy passes and add to their Travel Wallets, which allow riders to pay by trip, around the same time, Busch said. The region also anticipated nasty winter weather that ended in a bust.

Some passes and Travel Wallet funds were able to be loaded, while taps from customers with either already on their cards were recorded normally, he said.

Thousands of Key cards also expired Saturday, though Busch said the latest wave didn’t appear to be a “major factor” that contributed to Monday’s woes.