So on two machines running Ubuntu 26.04, the desktop client stopped syncing. I was not logged in and when I tried it failed. Normally pops a browser window to authenticate. It shows logged out, But when I click login I don’t get a chrome window to enter my credentials like it used to. Nothing happens. Access using chrome to the same nextcloud instance worked fine.
- New Root CA: On July 1, 2026 (3 days ago), my SSL certificate for my domain was renewed. It was signed using Let’s Encrypt’s brand-new “Generation Y” RSA certificate hierarchy. The intermediate certificate is called YR2 , which chains up to their new root Certificate Authority named Root YR .
- Missing Trust: Because Root YR was created recently, it is not yet included in your Ubuntu system’s built-in ca-certificates trust store.
- Chrome vs. System OpenSSL: Google Chrome uses its own internal, dynamically updated root store (the Chrome Root Store), which already trusts Let’s Encrypt’s new roots. However, standard Linux tools ( curl , openssl , and Nextcloud Desktop
Client via the Qt networking library) rely strictly on the local system trust store ( /etc/ssl/certs/ ), which throws a Verification error: unable to get local issuer certificate (20) and aborts the connection silently. - No Login Dialog: Because Nextcloud’s connection to my domain is aborted at the SSL level, clicking “Log In” does absolutely nothing (it never initiates the login because it doesn’t trust the server).
Solution A: The Client-Side Fix (For Linux Users)
I solved the problem with some AI help. I ran this simple terminal one-liner. It downloads Let’s Encrypt’s new root certificate, registers it into your system’s trust store, updates OpenSSL, and restarts the Nextcloud client:
curl -sSL https://letsencrypt.org/certs/gen-y/root-yr.pem | sudo tee /usr/local/share/ca-certificates/letsencrypt-root-yr.crt >/dev/null && sudo update-ca-certificates && killall nextcloud 2>/dev/null || true ; systemd-run --user nextcloud 2>/dev/null || nextcloud &
After that the desktop client immediately started syncing. My understanding is this only effects linux systems using recently issued let’s encrypt certificates.