I found a bug

ProtocolFilters supports generating debug logs.

To generate the log replace ProtocolFilters.dll with a version from Release_c_api_logs or Release_logs (depending on C or C++ API is used) and reproduce the problem. C# and Delphi wrappers use ProtocolFilters with C API.

The debug log will be written to ProtocolFiltersLog.txt in the same folder with the executable. Send it with a description of the issue to support@netfiltersdk.com.

The debug build starts writing log automatically. It is possible to start and stop writing the logs using API functions pf_startLog/pf_stopLog, for example to save several log files and control their size.