Upgrading from 5.7.5.13 to 8.1.0; stacks lost

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Hi,

i have tried upgrading to concrete 8.1.0 but in the process I have lost all my stacks.

I have four languages and each language has 200 stacks.

How can I avoid loosing the stacks and the references to the pages where they have been added.

Thank you very much.

arael78