[Bug] Android App: PDF annotation delays between input and completion of action

edited August 2, 2025
Hi. I just got access to the app last week. Thank you so much. It looks great and will really improve my workflow.

Issue description

I have found one issue which seems to manifest consistently. When I annotate a PDF, there is often a significant delay (up to 30s sometimes) from when I trigger the action to when it is concluded.

For example:
  • I will select the annotation button on the menu. The bar with options will appear (fone). I click the highlight option (fine), then I drag across the text to highlight. The drag colour shows, but then it will lag for an extended period of time before the text is actually highlighted.
  • I select the draw option from the annotation menu, then try to write something on the PDF. It might write a small amount, but then it will stop. I carry on doodling for a bit with no response. Then, a while later, the scribbles show on the screen.
It seems like the entire app freezes during these lags. It's almost as though it has to write to an online database on each action, rather than working locally, as the latency is extensive and unfortunately makes this aspect of the tool unusable, which, for me, is frustrating as it's the main reason I need the App.

Steps to reproduce:

  1. Open a PDF article from within the Library
  2. Select the annotation option from the meny (1 in Fig. 1)
  3. Select highlight (2)
  4. Draw over the text to highlight (3)
There will be a delay after point 4.
Alternately, select any other option such as (4 on Fig. 1) and the same response will manifest.

Environment

  • I am using a Samsung Galaxy S23 Ultra with the S-Pen, as well as a Samsung Galaxy Note S10 FE, also with S-Pen. So both are pretty good ito performance.
  • The issue manifests whether I'm using the S-Pen or my finger.
  • Network is high-speed broadband (1Gbps).
Screenshots
See screenshot from phone below (Fig. 1)
https://s3.amazonaws.com/zotero.org/images/forums/u1476172/khozbtgjffdpok5j1hrv.png

I hope this helps clean up some of the residual bugs. The app is great, and if this feature was working properly my research process would be so much better.

All the best
A
  • edited August 31, 2025
    The second issue mentioned here (slow drawing) seems to be the same as the "freehand drawing in PDF slows down" reported in https://forums.zotero.org/discussion/124295/android-beta-freehand-drawing-in-pdf-slows-down-occasionally-crashes-app (I experience the same problems as shown in the two videos in that report), and still affects the current stable build.

    Edit for cross-referencing: I've posted a bug report of the second issue, with Debug ID, here: https://forums.zotero.org/discussion/126421/debug-id-d918391774-android-app-freehand-draw-slow-and-wrong-rendering
  • I have the same problem in my Lenovo Idea Tab (released 2025). When using the pen it is impossible to draw anything.
  • I wonder if there is any update on this? I tested again this December with the same outcome from two new Android devices.
  • My experience highlighting text on Android is *frustrating*. Sometimes it works on the first try, but most of the time I have to try 4, 5, 6... or more times before it works.

    However, the freehand option works very well for me. In fact, sometimes (when it's impossible to highlight on the tablet) I circle the text by hand, so I remember to highlight it later on Windows.
  • I have the same problem on my Onyx Boox Air : handwriting notes on the pdf is extremely slow, even when writing slowly, the actually show trace lags one letter behind. On the native Onyx pdf reader the response is immediate, without any delay noticable. This makes handwritten commens on the pdf completely unuseable for me. Which is a pity, because I really like my workflow of synching to-read references and then read and commet and tag them on the tablet. Well done !!!!
  • Just chiming in that this is a persistent problem for me as well.
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