For what it’s worth, I’ve found no end of problems on Windows from other anti-malware and anti-virus software (but especially from McAfee and Malwarebytes).
Microsoft’s Windows Defender is free, ranks highly for malware and virus detection, and plays nicely with PhotoStructure.
Can you try switching to Windows Defender temporarily and see if that fixes the slow sync issue? (Don’t just disable McAfee, though: I’d hate for your system to be vulnerable during this test).