Package: curl Version: 7.64.0-4 The current Curl version in the buster 10.1 release contains a bug about the timeouts when used with SFTP If you set a timeout the listing will use exactly that much time to be completed ...
They already detected and fixed this problem in 7.64.1 see:https://github.com/curl/curl/issues/3506 I suggest backporting that version or the commit fixing the problem. I am using Linux dev16 4.9.0-9-amd64 #1 SMP Debian 4.9.168-1+deb9u5 (2019-08-11) x86_64 GNU/Linux <https://github.com/curl/curl/issues/3506>
