The setup is Bootcamp-installed Windows 7 Pro x64 on an old Macbook Pro 2011. When there's another WiFi device on the same network, my connection chokes up once every 5-10 minutes for 30-60 seconds, then resumes. The WiFi card is Mac's native, BCM4331 802.11n (VID 14E4 DID 4331) running under Bootcamp-supplied, latest ver. 18.104.22.168 driver—the same as on Broadcom's site.
I tried tinkering with all relevant (BT coexistence, 20/40 Mhz, etc) settings in both device properties and on the AP, no difference. In macOS and Ubuntu the same card works without a hitch out of the box, not a single packet dropped.
How do I pinpoint the cause?