Stale file handle error when using SMB3

I am using a fritz.box NAS in my local network and want to mount the storage during reboot. I used to successfully mount and use it using SMB1 but as it is not considered secure anymore I opted to upgrade to SMB3. The router supports this option and it is by default activated.

Here's my /etc/fstab line for the mount:

//<ip>/FRITZ.NAS/ /home/<me>/nas cifs credentials=/home/<me>/.smbcredentials,vers=3.0,uid=1000,gid=1000,iocharset=utf8,sec=ntlmssp 0 0

It successfully seems to mount as I can cd into the nas folder and navigate around. But once I try to access files, e.g. cat a text file, I get the Stale file handle error. E.g.:

cat: file.txt: Stale file handle

I also tried using vers=2.0 but that gives me the same results. I also checked /etc/samba/smb.conf and both client min protocol and server min protocol are correctly set to SMB2.

I set log level = 3 and logging = syslog in /etc/samba/smb.conf. Upon sudo mount -a it seems to simply get stuck. It just prints this.

CIFS: Attempting to mount //<ip>/FRITZ.NAS/

With SMB1 I get a successful message.

Not sure what else I should try.

Edit:When I try to execute cat file.txt the logs say:

CIFS: VFS: bogus file nlink value 0