This problem seems to still exist for me, on my iPad Pro 11" running LR 7.1.0. (Canon EOS-R, RF24-240 lens).
Edits made on the desktop with LrC 11.1, and Lightroom on the web, have no problem, so the Smart Previews synced to the cloud are just fine initially.
However, as soon as I open one of the Smart Previews in LR on the iPad, and make an adjustment, the lens profile artifacts are immediately shown, even if I undo or cancel my changes. However, the same image back in LR Web or LrC on the desktop is fine (even after changes, the Smart Previews look fine in LR Web, and the changes sync back to the desktop without the artifacts). So it definitely seems to be a preview rendering issue on the iPad itself.
Setting status to acknowledged. Attaching bug number. I'd found this on Dec 23rd and had already written a bug for it. These were my repro steps: Create Tiff file from Raw by Edit in PS (LrC) Sync (Smart Preview) Edit Tiff file by Edit in PS (Original) (LrC) (Obvious Edit - e.g move a composited layer Allow changes to sync Inspect in LrC after Sync - Is version from step 3 Inspect in LrW - is version from step 3 - verify zoom to greater than fit is still version 3 Inspect in LrA - i...