Mounted ExFat Disk: No such file or directory

I'm using an ExFat external disk on Ubuntu 18.04.4 with auto-mount but after a while I can't copy or edit items on the disk anymore but the items are still accessible.

After a system-restart I can write to the drive again.

Followed steps:

1 - sudo apt install exfat-fuse exfat-utils
2 - sudo mkdir /home/user-folder/NETWORK-HDD
3 - Edit sudo nano /etc/fstab
4 - Add line: UUID=****-**** /home/user-folder/NETWORK-HDD auto defaults 0 0
5 - sudo mount -a

Be advised that I'm not an expert in Linux, just started using it.