Hi wbk,
Thanks to your reply I have figured it out!
I had recently reinstalled Nextcloud due to the issue I describe in this thread
This led to a reset on all authorized clients. A nextcloud android app with auto-upload enabled was making endless authentication attempts causing a fail2ban block on the IP, in this case my router’s IP which was sending all the LAN requests due to hairpin NAT. I was able to discover this as the issue followed that android device.
I had considered fail2ban before, but based on this YunoHost documentation page, and SSH being unaffected led me to rule it out initially as I believed that fail2ban only affected SSH connections, which is not the case.
Manually removing the IPs from jail (as well as adding a whitelist entry for my router’s IP for future resiliency) has solved the issue.
I have also removed my local DNS server so that I have 1 less service to manage, but I am sure it would have continued to work fine with it in place.
I will report back if I run into further issues, but I do not expect any.
Thanks to everybody for their help it is greatly appreciated!