Refactor / rename not working, or stops working

When I rightclick a method name or function name, I have the option to Refactor - Rename...

I can fill out the dialog, but no matter the options I select, once I click 'Refactor' or 'Preview', the dialog closes and nothing happens. No error message, nothing in the event log, no change to the source.

The subject says 'stops working' because restarting the IDE seems to fix the problem. Note that in all cases where I've encountered the problem, I had multiple projects in separate windows of the IDE open - not sure if that affects it though (it's just very common for me).

PyCharm 2017.3.2 (Professional Edition)
Build #PY-173.4127.16, built on December 19, 2017
Licensed to Jaap van der Velde
You have a perpetual fallback license for this version
Subscription is active until February 12, 2019
JRE: 1.8.0_152-release-1024-b8 amd64
JVM: OpenJDK 64-Bit Server VM by JetBrains s.r.o
Windows 7 6.1

I've also recently started noticing extreme lagginess of my entire PC when PyCharm is open, but I'm suspecting recently replaced anti-virus of causing this problem. So, only mentioning it if it helps in identifying my refactoring issue. The anti-virus doesn't stop the refactoring from working initially, so I don't think there's a direct causal relationship there.

Cheers, JAAP.