Problem
If you have thousands of audio plug-ins, they happen to be re-scanned every time Synfire is started. Users with up to 3,000 plug-ins reported this.
Cause
A process that is waiting for the scan to complete probably times out, so the final result is not properly saved to disk. This seems to be specific to macOS. This is a known problem. The default scan at startup is currently not robust for this many plug-ins due to a timeout issue.
Solution
Please update to Synfire 2.2.1 Build #3 or later. We improved the scanner to run multiple plug-ins in parallel which is now up to 800% faster and less prone to timeouts and other issues.