Hi,
since you’re using Lubuntu, it’s quite likely that your system includes an older version of the Nextcloud desktop client, especially if it was installed from the default repositories. Older versions can sometimes cause sync issues, particularly when paired with a newer version of the Nextcloud server.
First, I recommend checking which version of the client you currently have installed. You can do this by running:
nextcloud --version
If it turns out you’re using an outdated version, I suggest downloading the latest AppImage version directly from the official Nextcloud website:
Download and install Nextcloud
Latest Appimage is v3.16.2 at the moment.
The AppImage client can be run without installation and won’t interfere with your system setup.
After updating, check if the sync issue persists. If it does, the problem might be related to a specific file, configuration, or even server-side limitations—but let’s rule out the outdated client first.
A similar issue was recently discussed here as well, and might be worth looking at for reference:
Linux Nextcloud Client response slow? - #2 by vawaver
Let us know how it goes!