The guard around the pynvml import was written as
except (ImportError, pynvml.NVMLError):
but when the import is what failed, the name pynvml is unbound, so
evaluating the except clause raises NameError — which that clause does not
catch. The handler blew up in precisely the situation it existed for:
Linux or Windows without pynvml installed.
It propagates out of the collector's constructor into monitor_loop, which
runs as a bare create_task, so nothing reports it beyond a "Task exception
was never retrieved" at GC time. The monitor just never produces data, and
running stays True, so a later start() takes the already-running branch.
Catch Exception instead, and wrap the loop so any failure is logged and
running is reset.
kk8bit