FTP file listing slow, Nextcloud makes new connection on each read

Steps to reproduce 1. create an FTP (or FTPS) Share in External Storages settings 2. browse to FTP folders in Nextcloud 3. look at ProFTPd logs while browsing Expected behaviour Once an FTP connection is established, it should be maintained for the duration of the session. However, Nextcloud immediately closes the session after a directory listing. This results in delays due to the connecting needing to be re-established as the user browses folders. When connecting from an external client (Filezilla), listings are much faster as the session is left open. Actual behaviour New connection established for each folder retrieved. The session is not left active. Disabling previews does not change the behaviour. Server configuration Operating system: Debian Jessie Web server: Apache2 Database: MariaDB PHP version: 7.0 Nextcloud version: 12.0.1 Updated from an older Nextcloud/ownCloud or fresh install: Updated from V.11 up Where did you install Nextclo…