I had unexpected results on my frontend app when I have tried to paginate backward.
I'm using the demo project to reproduce this issue.
Considering data:

When paginating forward I get endcursor with value "Mg==" which is expected.

Then try to get previous node with arguments (last:1, before: "Mg==") and expecting to get entity with id = 1. As you can see I get correct node with previous cursor "MQ==", but id of entity is incorrect.

If I try to get 2 entities instead of 1, the returned cursors are kinda "shifted". Entity with id=1 has cursor "MA==".

I think it has something to do with cursor computation when using 'last' argument.