I imported this example flow, which contains a subflow, but the subflow does not appear in the palette. The result is that I cannot delete it. I can see that it is there in the flows file. I have tried restarting node-red and flushing the browser cache.
Welcome to Node-RED
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25 May 14:15:30 - [info] Node-RED version: v1.0.6
25 May 14:15:30 - [info] Node.js version: v12.16.3
25 May 14:15:30 - [info] Linux 5.3.0-53-generic x64 LE
25 May 14:15:30 - [info] Loading palette nodes
25 May 14:15:31 - [info] Worldmap version 2.3.10
25 May 14:15:31 - [info] Dashboard version 2.22.0 started at /ui
25 May 14:15:31 - [info] Settings file : /home/colinl/.node-red/settings.js
25 May 14:15:31 - [info] HTTP Static : /home/colinl/.node-red/static
25 May 14:15:31 - [info] Context store : 'memoryOnly' [module=memory]
25 May 14:15:31 - [info] Context store : 'file' [module=localfilesystem]
25 May 14:15:31 - [info] User directory : /home/colinl/.node-red
25 May 14:15:31 - [warn] Projects disabled : editorTheme.projects.enabled=false
25 May 14:15:31 - [info] Flows file : /home/colinl/.node-red/flows_tigger.json
25 May 14:15:31 - [info] Server now running at http://127.0.0.1:1880/
25 May 14:15:31 - [info] Starting flows
25 May 14:15:31 - [info] Started flows