I've figured out the root cause: the Chromecast TV adapter was connected over a power line adapter (Extollo), which created connection problems. Not sure what exactly inside the power line adapter caused the connection problems, but after I connected with an Ethernet wire to the MX67, it worked again. To be clear the power line adapter worked fine for streaming, but somehow interfered with the Chromecast protocol preventing it from showing up in my streaming Apps on my smartphone. Thanks for all the responses.
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