Customers using Charles Schwab's thinkorswim trading app reported technical problems starting shortly before the market opened Monday.
Outage monitoring site Downdetector indicated over 500 problem reports for TD Ameritrade, the Schwab-acquired brokerage containing thinkorswim, around 9:30 a.m. Eastern time.
The numbers had slid to under 100 about 15 minutes later, according to Downdetector, which reported issues with trading and online brokerage.