Sorry, the bug tracker is for working on Python bugs, not on bugs of your programs written with Python.

The behavior of subprocesses running is tested intensively, scenarios like you described works well.

I don't know sockfish protocol but highly likely the problem is in communicating with the program.
For example, are you sure that sending `uci` without endline is enough to start processing the command?

Tools like ProcMon https://docs.microsoft.com/en-us/sysinternals/downloads/procmon or WinDbg can help with understanding what data is actually received by a process and what is sent back.