Accessing your Nextcloud Files through Webdav (https) can be quite slow due to the protocol and/or your upstream connection of your nextcloud to the web. It seems to me that if you “mount” the official webdav-path nextcloud is offering into KODI your files are routed through the Internet even when KODI and NC are implemented within the same network. Exchanging the URL with your local NC IP Address and switching to webdav (http) in order to avoid certificate problems is possible but has a negative impact on the speed (i dont know why though).
Accessing your files can be done much faster with creating an NFS-Share on your Nextcloudserver.
sudo apt install nfs-kernel-server nfs-common sudo vi /etc/exports
Add and alter following line:
and open your firewall ports (111 and 2049 for NFS and a fixed port for mountd):
the restart your services
sudo service nfs-config restart sudo service nfs-kernel-server restart
Check if your NFS share is visible:
showmount -e IP-address_of_NFS_Server
Et voilá: you can now explicitly (!) add a new network source to KODI. The NFS Browser still doesn’t find the share but mounting it manually does the job.