I have Windows 10 Pro 64 bit, and believe there is a bug with Process Monitor Portable 3.33. This is a new, standalone installation (I am not using the Portable Apps Platform).
It concerns the "File system activity" component only; everything else seems to work fine. When running ProcMonPortable for the first time, things behave as expected. But if ProcMonPortable is closed and restarted, no file activity is recorded whatsoever, even if all filters are reset (or deleted!).
I first tried deleting my settings folder, and then deleting ProcMonPortable completely and reinstalling it. Neither worked.
What did work temporarily was rebooting my PC. File activity was recorded fine until ProcMonPortable was closed and restarted, at which point the bug returned just as before.