Frequently Asked Question
We've only had this occur once on a customer system and we couldn't reproduce it here in-house, but the customer (all respect to Martin S!) found the solution and we're documenting here for others to find if they run into the same issue.
The behavior is that Olga's UI would display as black in a correctly-sized plugin window. The plugin itself would work, and you could switch to Logic's Controls view and manipulate parameters, but the plugin UI itself would just display as black.
In this case the solution was to manually uninstall EVERYTHING related to that plugin, including entries from /var/db/receipts and ~/Library/Audio/Presets/Schwa/Olga/. Deleting those, rebooting, and then reinstalling the plugin from scratch and rebooting again fixed the issue.
Please note: Tinkering around in /var/db/receipts is not for the faint of heart, and can cause significant problems with other software - make sure you only touch files such as com.Schwa.PLUGIN_FORMAT.pkg.PLUGIN_NAME.* or com.stillwellaudio.PLUGIN_FORMAT.pkg.PLUGIN_NAME.* and make sure your system is backed up before proceeding. Proceed at your own risk.