First noticed with an insync google drive folder automatically labelled as firstname.lastname@example.org. Catfish will not search this folder unless "show hidden files" is selected.
To test I created another folder "he.llo", and catfish's behaviour was the same.
1.4.2-0ubuntu1 (via catfish maintainers ppa)
Sean Davis referenced this bugreport in commit 8b3fe1149562195b33f73825db21e231caa5aea7
Improve hidden file logic (bug #14497)
Fixed in the above commit.