Fun fact: If I switch between being in developer mode and not (at chrome://extensions) and reloading the site - everything loads perfectly. But second time loading the site, same problem occurs again (regardless of developer mode on/off).

Can you provide us a input trace?

This is likely to do with the fact that scrollbar dragging is main thread driven whereas the other methods of scrolling you describe are compositor thread driven. And that priority goes to the compositor thread in handling scrolling. So this would be working as intended. There are policies around the mouse being down as well.

But we'd ned to confirm from a trace. If you provide a sample URI then we can see how it behaves in other vendors too.

Here's a simplified version of what I am building: http://iliketoplay.dk/public/lazyload/

1: Listen to scroll event
2: Check if element is in view
3: When in view: load image
4: When loaded: fade in.

Thank you for providing more feedback. Adding the requester to the cc list.

For more details visit https://www.chromium.org/issue-tracking/autotriage - Your friendly Sheriffbot

Thanks for the repro case. It seems to be working correctly here. Would you mind recording a trace[1] of the problematic case for us to look at?

[1] https://www.chromium.org/developers/how-tos/trace-event-profiling-tool/recording-tracing-runs

Problem is that this is very inconsistent. Problems mostly occur with sites I have reloaded many times (working on frontend development).

we have the exact same problem at https://www.heise.de

If I scroll with a TrackPad or a MagicMouse, all lazy loaded images are in state "pending" for 3 seconds in two out of three times (you see three dots while loading) and than got to "(state from cache)". If I drag the scrollbar, all images are loaded instant.


my chrome: Version 65.0.3325.162

Same exact issue here: https://dot-agency.it/spctrm/
Very inconsistent as well.
Tried lazysizes, unveil and even tried a super simple src swap and load.
No success the problem remains, only in chrome my version 65.0.3325.181

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It sounds like the heuristic which blocks tasks for smoother scrolling. We're planning to remove this logic in 874836.