Similar issue here with my QHY174GPS (single camera): after the first recording of a stream the warning "Recording device is busy" appears and no further image or stream acquisitions are possible. The behaviour is fully consistent.

Note: in oder to get the camera alive again connect/disconnect of Ekos, or stop/start the driver from INDI web manager, with camera power off/on in between had no effects. Only rebooting the rasp Pi worked.

From the log window:

2021-12-09T08:27:02: [WARNING] Recording device is busy.
2021-12-09T08:26:43: [INFO] Starting video streaming with exposure 0 seconds (50 FPS), w=1920 h=1200
2021-12-09T08:26:37: [INFO] Recording stream has been disabled. Closing the stream...
2021-12-09T08:25:52: [WARNING] Recording device is busy.
2021-12-09T08:25:40: [INFO] Waiting for all buffered frames to be recorded
2021-12-09T08:25:36: [INFO] Starting video streaming with exposure 0 seconds (50 FPS), w=1920 h=1200
2021-12-09T08:25:36: [INFO] Record file is /home/pi/capture/indi_2021-12-09/indi_record_2021-12-09@08-25-36.ser
2021-12-09T08:25:36: [INFO] Starting video record (Duration): 1 secs.

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