Created attachment 149426 [details]
ODT document with laggy bulleted lists

The bug occurs in this version:

Version: 6.2.0.3
Build ID: libreoffice-6.2.0.3-snap1
CPU threads: 4; OS: Linux 4.15; UI render: default; VCL: gtk3; 
Locale: en-CA (en_CA.UTF-8); UI-Language: en-US
Calc: threaded

But not in this version:

Version: 6.0.7.3
Build ID: 1:6.0.7-0ubuntu0.18.04.2
CPU threads: 4; OS: Linux 4.15; UI render: default; VCL: x11; 
Locale: en-CA (en_CA.UTF-8); Calc: group

I have a document with lots of bulleted lists under various headers. 

Whenever I perform any of the following actions:
- insert a bulleted list item
- delete a bulleted list item
- reorder a bulleted list item using Alt + Shift + Up (move up) or Alt + Shift + Down (move down)

The following happens:
1. soffice.bin CPU usage jumps to 100% for about a second
2. the UI freezes for about a second

This happens in web view, but not in normal view.

This happens with numbered lists and paragraphs as well.

This is mildly annoying because if I need to insert a bunch of row items in quick succession, the output becomes all garbled because of the lag (and presumably because of how Ubuntu handles key presses). For example, if I type "one <lf> two <lf> three <lf> four <lf> five <lf> six <lf> seven <lf> eight <lf> nine <lf> ten" in quick succession, LibreOffice slowly finishes printing this out on the screen, several seconds after I finish typing:

> • one
> • tw
> • othe
> • reforu
> • fv
> • eisi
> • sxevneei
> • gh
> • tnn
> • eiten

(do not want)

In web view: If I select everything in the document, cut, and paste, then bullet lists become fast again. But after I save and then reopen the document, it becomes laggy again.

The lag doesn't seem to occur if I create a new document with a fairly small bulleted list. If I save and reopen, then it's still speedy and responsive. If I paste in the 46 pages of bulleted lists from the laggy document, it's still not laggy. But after I save, close, and reopen, then it becomes laggy.

Also:
- Lag occurs in Safe Mode
- Lag occurs whether or not OpenGL is enabled
- Lag occurs whether or not Navigator is open
- Lag occurs regardless of how long the document has been open (i.e. even after the document has finished paginating)

I've attached a document where the lag happens for me. Excuse the screaming; I've anonymized it with a's.