Can't add new file to directory starting with underscore

[BardlyThere]

FastHub Version: 4.6.7
Android Version: 9 (SDK: 28)
Device Information:

• Manufacturer: Google
• Model: Pixel

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I've got a few Jekyll sites I'm working on and the app keeps telling me _name isn't a valid extension whenever I try to create files in that directory.

[textplusdata]

There are several comments on the same issue.i had same problem today.