Had same issue.
Kubuntu 19.04 VM running on Virtualbox Version 6.0.14 r133895, upgraded via instructions on https://help.ubuntu.com/community/CosmicUpgrades/Kubuntu as of 28/10/2019
SATA controller with dynamically allocated .vdi file set as storage, non encrypted.
Had same issue.
Kubuntu 19.04 VM running on Virtualbox Version 6.0.14 r133895, upgraded via instructions on https:/ /help.ubuntu. com/community/ CosmicUpgrades/ Kubuntu as of 28/10/2019
SATA controller with dynamically allocated .vdi file set as storage, non encrypted.