SarcasticSparrow10 , please note that during the upgrade you do NOT copy /opt/clearml/data/mongo into /opt/clearml/data/mongo_4 , you create the folder like in the instructions: sudo mkdir /opt/clearml/data/mongo_4

This is the reason that it is giving out errors - You've got old mongo data in your mongo 4 folder...

Please follow the instructions to the letter - this should work 🙂