@giomasce I tried to recreate the problem that you are having now, and I did not have success. I did the following steps:
1 - I created a VM with Debian 10 and kernel 4.19.132-1.
2 - I make a new disk (dd if=/dev/zero of=/testing)
3 - cfdisk /testing
4 - mkfs.ext4 /testing
After to have a disk that I could mount and umount whenever I needed.
5 - I started Netdata
When I access the dashboard all the disks were there. I closed the dashboard
6 - After few minutes I ran : mount /testing /mnt
7 - I access the dashboard again.
The disk was there, it was identified to /mnt
8 - I closed dashboard and I ran umount /mnt
9 - I opened the dashboard and the disk was not more there.
I did everything using the newest Netdata compiled from the source. Considering everything I executed, I have few doubts for you:
1 - How did you install your Netdata?
2 - What is your Netdata version?
3 - Are you using the default configuration? Or did you change the parameter memory mode?
Best regards!