startup stops on loading screen with flashing pencil icon - missing dependency

[mikedlr]

• Operating system: Linux / Ubuntu 18.04.5 LTS
• Pencil version: 3.1.0 (development branch)

If I follow the install instructions then pencil gets to the loading screen and then stops. There's a message about a missing dependency but nothing aborts.

Expected: Pencil should load as normal or, if some dependency is missing then it should abort and say what's missing.

I put a fix into a pull request: https://github.com/evolus/pencil/pull/654