Hi @attila,
(Re accepted answer)
That's solved it!
I made the szerr.value modification, and did not get any error messages. But your example code (which runs perfectly!) helped me realize why: I think the issue isn't from the dwf library.
My device connection step (FDwfEnum) was much more complicated than what you posted - I had originally based it on the Enumerate.py example, since I needed the device serial numbers and thought the other debug information might be useful.
When I modified my device connection step to use only the dwf library (cutting out most of the Enumerate.py example - anything related to dmgr, ftd, and dftd), suddenly my old code worked perfectly. It's still beyond me exactly what was causing the issue, but it looks like the revised connection procedure has fixed it.
Thank you for your patience in helping me sort through this. I hope this thread helps someone who finds themselves in similar shoes!