Upgrading from an older version than 3.4.0 requires upgrading to 3.4.0 first. Below are the instructions on how to perform the upgrade.
SSH to your Unomaly instance. In the menu, type 7 to "exit to system shell", and enter.
First start a screen session as this upgrade may take a long time with several database migrations:
screen -S upgrade
Remove the flag file if you tried upgrading to the newest version and it failed:
sudo rm /DATA/unomaly_UPGRADING
Download 3.4.0 and install it (this will take a while):
sudo sh unomaly-3.4.0.run
Finally update to the latest version (3.6.0 in this example):
sudo sh unomaly-3.6.0.run
Upgrading to the more recent versions should work correctly after this.