These errors can be returned if there were changes made to Variational data after the Product was listed on eBay and had sales.
According to eBay requirements, it is not allowed to change the Variational data (e.g. the name of Variations or options by which it varies (e.g. Color, Size), the number of Variations, etc.) after the Product was listed on eBay.
When you list a Variational Product on eBay via M2E Pro, eBay remembers its initial listed state on the Channel. Thus, if any of the Variational data changes in Magento, M2E Pro or on the Channel, the connection between the eBay Variation and the related Magento Associated Product is disrupted. As a result, the Product can not be revised and the errors you have faced are returned instead.
To avoid the errors, you need to change the Variational data back to its initial state, like it was when first listed on eBay. Make sure all options/variations are the same as they were when the product was listed. Also, check the options titles. The quantity of the variations should be the same in Magento, M2E Pro, and on eBay.