If a plugin file has moved or crashes in Studio One, it will end up in the blocklist as a result. Fortunately enough, this can be resolved in a few simple steps:
1. Navigate to Studio One's preferences
2. Click into the Locations > VST Plugins tab
3. Next, ensure that the "Scan at startup" option is enabled and click Reset Blocklist
4. Now, restart Studio One. Studio One will rescan all of the plugins again and will this time include plugins that were recently in the blocklist.