Hi All!
There is a handy customization mechanism in how tiddlers are saved to the filesystem by the node backend using $:/config/FileSystemPaths.
Unfortunately, upgrading to 5.1.20 causes file names to be 'Filter error_ Missing [ in filter expression.tid', even using the verbating config from the above doc.
Reverting to 5.1.19, it works once again.
Sorry if this is a known issue.
Best,
Peter