If you are not using IPV6, could you try changing the pihole.toml to use only IPV4 ports ?
sudo nano /etc/pihole/pihole.toml
Find using CTRL+W word 80o and remove the [::] as well as [::]443os.
port = "80o,443os" ### CHANGED, default = "80o,443os,[::]:80o,[::]:443os"
Restart pihole-FTL usin sudo systemctl restart pihole-FTL.service
Set new password if you're re-installed it in your previous attempts but you should see the interface.