If you are using the stock 5.4 kernel this is normal but I can confirm it is fixed in newer 5.8 kernels.
To fix it just install the 5.8 kernel and reboot:
sudo apt install linux-headers-5.8.0-64-generic linux-modules-extra-5.8.0-64-generic linux-image-5.8.0-64-generic........
This is a great way to use your ftp server space, for example on your web hosting account (althoughI believe many hosts don't allow storage like this), but if you have a VPS/Dedicated Server etc.., this would be perfect. Imagine how easy it is to work with an ftp account that you can just mount as a normal partition or directory in Linux, it would be great for backups etc..
Name
curlftpfs - mount a ftp host as a local directory
Synopsis........