Our office machines just received the Revit 2020.2 update along with Dynamo 2.3 which came with the update.
What happened was that Refinery extension disappeared in Dynamo window. I was testing Refinery v35.
When I asked the IT to re-install to bring back the Refinery, no luck. Revit still has the Refinery under Add-Ins tab which is great but, I couldn’t see it in Dynamo window as extension. (for exporting the script)
Basically, what I had to do was find the previous Dynamo version package folder to locate Refinery package and copied to the current Dynamo version package folder manually. (C:\Users*username*\AppData\Roaming\Dynamo\Dynamo Revit\2.3\packages)
It brought back the Refinery extension in Dynamo finally!
I hope this helps for users experiencing same situation.