This issue can happen for different reasons depending on your operating system:

1. Windows

- Go to Settings > Display.

- If a monitor is not detected, check if both EDIDs are recognized.

- Manually enable the missing display if it appears disabled.

2. macOS

- macOS only supports Single Stream Transport (SST). This means it can only send one video signal at a time, even if multiple monitors are connected.

- macOS uses the EDID of the primary monitor to determine output. If the connected monitors have different specs, one may go black.

- For example: If a 2K@120Hz monitor and a 4K@60Hz monitor are connected, macOS may prioritize the 2K EDID and cause the 4K monitor to fail.

- Try adjusting the high refresh rate (e.g., to 60Hz) to help all displays work properly.

If you have any questions, please contact Anker Customer Support for further assistance.