Compute Plan does not compute

Hello All,

I have the same problem as described in this (resolved) topic: Confluence Migrator - Step 6 Nested pages error with Compute plan . But downgrading verison does not help. My screen is stuck, buttons are greyed out and eventually got another error message:
image

I have XWIKI on prem installation and want to migrate confluence from one server to another also on prem. Versions: Confluence Migrator 1.0.12, Nested Pages Migrator Application 0.7.5. Can you help please?