If overlapping between the APs is very high, sometimes client may get confused and unable to decide which AP is best, thus frequently roams between nearest APs.
Please note that roaming is totally a client UE decision and its driver configuration.
You can remediate this by changing BSS minrate to 12Mbps in WLAN setting and see if it fixes the issue.
Also it is worth checking if this system has a USB 3.0 device connected to it, because client is connected on 2.4 G radio and USB 3.0 devices cause interference on 2.4 G radio.
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