thanks for feedback and the explanation. I not really with prio one about the first topic, because that does not hurt so far.

I come to the second one as I have the traces of the whole INDI communication present: You're right, the driver also sends some "message" entries (not only for the CCD, but also other drivers). This happens during many (53) exposures only two times, when the exposure time is long (in the case 300s), if the exposure is short (2s) no message is transmitted. The two messages were in INFO state and report end of exposure and end of download.
So still the behavior is in this case strange. What do you think ?