Calling removeFiles on a filepond instance object, seems to only remove the first file and not all of them.
(Which would be the expected behaviour for calling removeFile (singular) without parameters )
Had the same problem. Docs says, that it's has an argument:[query], and no information about usage of empty args.
I found in Changelog 4.19.0 message about fixing problem: removeFiles({ revert: false }). So I tried this snippet, and it cleaned all images. I don't think that is the correct usage of { revert: false }, but it solves the problem.