Guy and Quentin,
I picked up a replacement today and it is still dodgy and in exactly the same sort of way. I can't run a comparison new against old though on Thursday I will be able to replicate some of the test scenes I shot the first copy on but today I shot another scene, a cityscape that I often use, and we have very blurry right hand side at 35mm and that shifts to the left at 70mm. For my own comparison I shot my 24-70 f4 lens on the same scene and though the f2.8 is better in the areas where it has achieved focus, overall at these focal lengths and especially at f4 and 35mm, the F4 lens absolutely trounces the f2.8 version. Simply no contest because the blur on the side at 35mm is so bad on the more expensive lens.
So that's two in a row now...
I'm away from base and LR has gone irreperably wrong on the only machine I have with me (it's an older machine and I can't update to a version that reads the A7RII files, patch fails) so these are exported from Photos to TIFF and imported into an older version of LR for viewing but no adjustments, then to JPEG for uploading. That means I haven't been able to sharpen etc as I usually would, but it's a level playing field between the two lenses at least. Take a look.
With the F4 lens
With the F2.8 lens
Both AF on the central mid-distance flat building with two windows. I will need to shoot these again with all due rigour on but I think it's clear the F2.8 lens has an issue, again....