shared folder in virtualbox guest debian 10 not showing files from linux mint host

I believe I have done everything all the manuals have said to get this to work, and have been struggling with it for a few days now. Here are the details of the setup: **Host:** Linux Mint 18.1 Serena, Ubuntu 5.4.0-6ubuntu1~16.04.4, 4.4.0-53-generic **Guest:** Debian GNU/Linux 10 (buster), 4.19.0-8-amd64 **Virtualbox version:** 5.1.38_Ubuntu **Guest Editions version:** 5.1.38 Guest Editions is installed in the guest, my user is part of the group vboxsf, in the gui of Virtualbox on the host, I selected a folder in the host home directory which I made called MintDebianSharedFolder and selected Auto-Mount, and gave the name to be seen by the guest MintDebianSharedFolder5. Now upon booting the guest (Debian 10): cardamom@ruthenium:~$ sudo ls -la /media/ insgesamt 14 drwxr-xr-x 4 root root 4096 Mär 24 12:41 . drwxr-xr-x 19 root root 4096 Mär 23 14:34 .. lrwxrwxrwx 1 root root 6 Mär 23 13:19 cdrom -> cdrom0 dr-xr-xr-x 6 root root 2048 Mai 9 2018 cdrom0 drwxrwx--- 2 root vboxsf 4096 Mär 24 12:38 sf_MintDebianSharedFolder5 cardamom@ruthenium:~$ sudo ls -la /media/sf_MintDebianSharedFolder5/ insgesamt 8 drwxrwx--- 2 root vboxsf 4096 Mär 24 12:38 . drwxr-xr-x 4 root root 4096 Mär 24 12:41 .. There are in fact 2 files in the corresponding folder on the host - **Why are they not showing up in the guest?** I created the second one just a moment ago on the host, but it is just not visible in the guest. Here is the output of a few other commands on the Debian 10 guest which may help diagnose: cardamom@ruthenium:~$ df Dateisystem 1K-Blöcke Benutzt Verfügbar Verw% Eingehängt auf udev 3354284 0 3354284 0% /dev tmpfs 674824 9084 665740 2% /run /dev/sda1 7578488 5697972 1475832 80% / tmpfs 3374108 0 3374108 0% /dev/shm tmpfs 5120 4 5116 1% /run/lock tmpfs 3374108 0 3374108 0% /sys/fs/cgroup tmpfs 674820 20 674800 1% /run/user/1000 /dev/sr0 58214 58214 0 100% /media/cdrom0 cardamom@ruthenium:~$ mount | grep sf sysfs on /sys type sysfs (rw,nosuid,nodev,noexec,relatime) cardamom@ruthenium:~$ sudo VBoxControl guestproperty get /VirtualBox/GuestAdd/SharedFolders/MountDir Oracle VM VirtualBox Guest Additions Command Line Management Interface Version 5.1.38 (C) 2008-2018 Oracle Corporation All rights reserved. No value set! cardamom@ruthenium:~$ lsmod | grep vboxguest vboxguest 299008 4 cardamom@ruthenium:~$ cd /opt/VBoxGuestAdditions-*/init cardamom@ruthenium:/opt/VBoxGuestAdditions-5.1.38/init$ ls vboxadd vboxadd-service vboxadd-x11 cardamom@ruthenium:/opt/VBoxGuestAdditions-5.1.38/init$ sudo ./vboxadd setup vboxadd.sh: failed: Look at /var/log/vboxadd-install.log to find out what went wrong. vboxadd.sh: Starting the VirtualBox Guest Additions. vboxadd.sh: failed: modprobe vboxsf failed. Any ideas much appreciated