Hi,
from my point of view the indiserver causes the problem due to the fact that QHY600 needs for it's images more memory. Out of the indidserver.log from my mount located pc I got the entry:

2021-08-08T09:45:30: Client 25: 105842564 bytes behind, shutting down

as this limit is coded in indiserver.c which is 128Mbyte 
The camera itself has with bin 1x1: 9600x6422 = 61651200 pixel including overscan etc. and the pixel are 16 bit. This makes 123302400 Bytes, so very close. If you take into account that you need to encode this binary values base64, the size expands about 30%. So if the image transfer starts at a point, when the image is fully received from the driver itself, the server is always more than this buffer size behind and shuts down.
If you are accessing the data without passing the server -> you are around this possible bottleneck.

@jasem: it would be nice if you could check this theory 
Michel

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