Did you add both FQDNs, one without and one including www?
This way I could access the website at ns8test.com and www.ns8test.com and I could reach the cluster-admin at ns8test.com/cluster-admin. (ns8test.com is the NS8 domain name)
IIRC this didn’t work when I tested it the last time, maybe the traefik update made it work.
Maybe unexpected but technically understandable: Clamav isn’t available for Nextcloud so the scan fails (which seems also executed before thumbnail generation) so the previews are missing.
In NS7 clamscan and clamd were available at OS layer so they could be used by other software than mail like Nextcloud.
In NS8 there’s no clamav in the Nextcloud container and the mail server clamav uses socket so it can’t be used by other software.
While it’s possible to install clamav in the Nextcloud container which makes antivirus and previews work, I doubt it’s a good solution as clamav needs a lot of ressources.
Clamav seems intended for mail scanning so there could be issues with false positives when scanning files but for sure it’s better than nothing.
Maybe we should create a clamav container to be used from other apps. 
See also Threatshield and CroudSec do not prevent / protect from malware (AntiVirus) at ALL! - #5 by stephdl