Thanks for sending the system information over Robert! I’ve set your reply to private just for it not to be publicly visible.
Everything looks good in the setup of the site, I don’t see anything that I can relate to the update problem you are experiencing. I have also tested that update (PRO 4.2.5 > 4.2.6) and everything went smoothly.
Could you perform a manual update? If you try the auto update does it still show that error?
Please let me know about it,
Best,
Nico