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Unfortunatelly I've just noticed that I don't have the logs/ directory in my witness_node_data_dir/ and I get main.cpp:119 error saying that "Error parsing logging config from config file ..., using default config" when I start steemd ...

That error is a known bug. It happens when you have multiple lines with the same keyword in the config file, like multiple "witness" entries.
Just ignore that error and redirect standard output + standard error to a logfile.

I'll try rebuilding steemd and check if at least that logging error will be resolved ...