Preview app on iPadOS 26 — handwriting "refine" and "straighten" tools breaking text + severe lag

Hi everyone,

I’m experiencing a serious issue with the Preview app on my iPad Pro (M2) running iPadOS 26 (Tahoe).

I mainly study using my Apple Pencil (2nd gen.) with PDF textbooks, so the new Preview app + handwriting "refine" and "straighten" feature sounded perfect for my workflow. However, the feature has been causing major problems that make the app nearly unusable:

1) Handwriting "refine" and "straighten" break text completely

When I write normally with Apple Pencil and enable the Refine Handwriting or the Straighten option, the app distorts my handwriting instead of improving it.

Example: if I write “ciao”, Preview might rewrite it like:

c i

a

o

So letters get spaced out, moved around, or placed on different lines. It looks like the refine engine loses alignment and completely destroys the original word structure instead of straightening or smoothing it.

2) Heavy lag during handwriting / annotation

After a short time writing on PDFs, Preview becomes extremely laggy.Strokes appear with strong delay, and scrolling pages becomes choppy, with .other major issues

3) Notes / annotations sometimes disappear or shift

In some cases, handwriting seems to “jump” or relocate on the page, and once or twice I’ve lost annotations entirely.

If needed, I can provide screen recordings.

Thanks a lot.