In a statement to Xperia Blog, the issue isn’t with the software packages nor the devices per se, but with the actual infrastructure used to deliver the update.
We’ve temporarily paused the Android 7.0 upgrade for Xperia XA and Xperia XA Ultra due to minor performance inconsistencies related to the over-the-air delivery system. Regardless of whether a user has been able to successfully run the upgrade or not, there is no detrimental impact on device performance or loss of existing user data. We’re aiming to re-commence the rollout as soon as possible with a seamless upgrade experience for all users, and will provide a further update in due course.
Software roll-outs in this space usually scale up between one and two weeks. The company probably had seen with universal version checks along the line that the OTAs were not being pushed out automatically and that the update wasn’t being installed in the proportion it was targeting.
In any case, it seems sort of redundant to say that something’s “on hold” when something else held it up in the first place. But from what it says, Sony’s intent on paying attention to its server tensions and serving you, the customer, right.