"Cannot find reference" using Python plugin

Since a couple of days ago I noticed that Intellij fails to find Python dependencies.

My settings/versions are:

• IntelliJ IDEA 2018.1 (Ultimate Edition)
• Build #IU-181.4203.550, built on March 26, 2018
• JRE: 1.8.0_152-release-1136-b20 x86_64
• JVM: OpenJDK 64-Bit Server VM by JetBrains s.r.o
• macOS 10.13.4
• Python Plugin: Version: 2018.1.181.4203.550

I tried a couple of times recreating the virtualenvironment and re-adding it but it didn't help.

In the following capture you can see that the dependency exists:

Also, following there're captures that the SDK is properly set to the project:

As extra information:

1. I've already tried invalidating caches and restarting the IDE
2. Found another user with the same issue: https://stackoverflow.com/questions/49140911/intellij-idea-says-unresolved-reference-on-everything-python-virtual-environ

Any help is welcome.

Thanks in advance.