In Process Explorer my GPU graph always shows 0% . I tracked it down to having specific engines selected, despite these engines being "busy" on the Engines screen. See: [System Information > GPU tab > Engines button] .
The "busy" engines (13, 19, and 22) were indeed checked, so I would have expected the overview GPU graph to display some usage, but it remained pegged on 0%.
Through trial and error I found that checking only the "idle" looking engine 9, the overview GPU would show up to 100% (as expected for a "busy" engine). I could not find any checkboxes that would correspond to the other 2 "busy" engines.
So something must be out of sync between the checkboxes and the graphs shown on the Engines tab.
I upgraded the SysInternals suite & Nvidia drivers to recent versions (both were ~2 years old prior to that). It made no difference.
Version details:
Process Explorer : 16.32
Windows 10 x64 : 10.0.18363 Build 18363
Video card: GeForce 1060 6GB
nVidia driver : 462.31
Engine 13 was performing usual display tasks. Engines 19 & 22 scientific computation via the BOINC client.