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TCP previous segment not captured and Dup ACK at regular intervals - what is going on?

My Wi-Fi bandwidth regularly drops from 144Mbs to 48Mbps (Windows 10, 802.11n). At the same time, the download speed temporarily goes to zero.

It does not seem to be hardware related - I have tested the USB dongle (https://www.amazon.fr/dp/B077X5Y2LT/) I use on another devices, and it works fine. Reinstalling Windows is also useless.

However, in Wireshark, I found that whenever the bandwidth drops there are "TCP previous segment not captured" and "TCP dup ACK" messages. What is going on?

Connection speed Normal bandwidth Dropped bandwidth Wireshark results when the bandwidth drops