Cause: the system detected that the booker's time zone is in US/Central. In order to prevent this, please remind bookers to ensure their time zone within their booking is set to US/Eastern.
This happened due to the feature Automatically detect booker timezone, you can disable this by going to Times & availability > Language & Timezones
This feature detects the booker's time zone, according to their browser and IP data. It can change, according to their ISP (internet service provider) or if they are using a VPN.