One of the 'esoteric' findings in the testing channel at Berkeley, and I can reproduce, is, that from W10 test build 16226, if the Task Manager is open to the Details tab, this tab only, even when minimized, BOINC seems to read this as system busy, or this leaks into the Mouse/Keyboard channel making BOINC think the system is in use (if settings are to suspend computing when in use). Short for: Don't let that CPU time eating tool sit on your desktop. Use MS' free Process Explorer instead, superior for performance analysis.

W10 is really an unstable platform, hard to know what was 'fixed', suddenly my internet went 'so so' to 'poor' under 16251 whilst using the bridged connection (1 computer linked via WIFI AC, other computers linked to this computer with Ethernet cable). Lots of experimenting, but forcing the WIFI from Auto to use the 5 GHZ band did the trick... everything is speeding now (strangely, this mostly affected the US sites and destinations, European not so much.)

Edit: Just witnessed a MIP1 task coming (they go at 11MB a pop), where before the 8MB element would arrive at 43-45KB, now saw 2.2MB download speed being registered.