In my PlutoSDR, the culprit for disconnecting was the middle USB connector (data pins were cold-joint soldered). Inspect the connector with a microscope or a very strong magnifying glass to check yours is well soldered. Mine wasn't.
Resoldered the connector under a microscope (also changed the USB cable with a shorter one), and now it's all good, no more randomly LAN connections disconnections.
Never used it with other OTG USB devices, or with an extra power adapter. Just the USB cable to the computer and the standard SDR firmware (with the frequency band unlocked up to 6GHz, and the second ARM core unlocked on the Zync).
LATER EDIT:
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Found out recently about a new SDR learning resource based on PlutoSDR and Python, will add the link here:
https://pysdr.org/It is a very comprehensive SDR course yet very easy to follow, it covers all the important aspects of SDR without flooding the student with math, and without going into very fine details. Has some practice and exercises, a few test questions, etc.
Parsed it recently, recommended.