I'm running into the same problem here as well - Tried completely nuking all preferences, keychain settings, following all steps posted above, removed entire app and all other system settings for HC- Reinstalled fresh, logged back in and the exact same problem occurs. It's been doing this for months now. Can anyone confirm if this'll be addressed? This is so impactful to workflow I'd almost rather use Slack to actually get work done. Hope it gets resolved soon.

I can confirm this too (On Mac HipChat app). Please fix this asap. Thanks!

I previously attached the window server crash I periodically experience as a result of this issue.  This occurs in both the HipChat app and the safari web app.

The problem might be triggered for me (or made worse) when the code block has lines that have been wrapped. 

I can confirm this issues as well and it is very annoying when trying to get things done.  I think Atlassian just wants everyone to switch over to Stride instead of fixing the problems that exist.

I can confirm the issue.

/pre workaround doesn't work with Linux client.

It's really problematic for dev teams such as ours. Any idea for the fix ETA?

Same issue here.

Can someone please take a look at this, @Atlassian team? This makes HipChat barely usable on High Sierra.

I'm seeing the same issue, scrolling with a code block on the screen is ridiculously laggy. I tried the above workflow (just steps 1 and 7), but it hasn't helped. One thing I did notice is that it's only laggy if the beginning of the code block is on the screen, if the beginning is hidden the scrolling returns to normal speed even if there the rest of the code block is still visible.

Keeping the code block minimized (not clicking "Show more") keeps the lagging to a minimum.

This behavior does not appear when using the /pre command. I attached a video to demonstrate what I'm seeing, I scrolled at the same speed (as best as I could) throughout the whole video. hipchat_laggy_codeblock.mp4

13 days later and the slowness is back.

More interesting issues, and a potential fix...

Found a particularly long code block in one of the private rooms I'm in, and it actually managed to (repeatedly) crash WindowServer just by scrolling past it. Trying to figure out what was wrong, I eventually decided to try to blow away all of my preferences (following the instructions https://confluence.atlassian.com/hipchatkb/mac-desktop-app-clearing-preferences-751436224.html) and this seems to have resolved the slow scroll issues. Specifically, I only followed Steps 1 (Close Hipchat) and 7 in the above, since we use SSO and I didn't think KeyChain would be involved:

At the command prompt, enter the following commands:

defaults delete com.hipchat.HipChat
rm ~/Library/Preferences/com.hipchat.HipChat.plist
rm -rf ~/Library/HipChat/
rm -rf ~/Library/Application\ Support/hipchat/
rm -rf ~/Library/Application\ Support/com.hipchat.HipChat
rm -rf ~/Library/Caches/HipChat
rm -rf ~/Library/Caches/com.hipchat.HipChat/
rm -rf ~/Library/Saved\ Application\ State/com.hipchat.HipChat.savedState
rm -rf ~/Library/WebKit/com.hipchat.HipChat

There's still a small amount of slowdown when scrolling past code blocks but it's orders of magnitude better, and totally livable, vs. what was happening before.

Note to anyone following this issue - it'll make you log in to HipChat again, so make sure you know or can reset your password before you proceed.

Interesting side-note - Safari also slows down significantly (although not quite as badly as the fat client) when trying to scroll past a code block on High Sierra. Chrome has no such issues, and scrolling is smooth even with code blocks in view.

More interestingly, while HC is attempting to scroll, I can't scroll any other window. I assume this is because the scroll gestures are being captured by Safari somehow.