SUMMARY
With the Aug05 krita-4.3.0-prealpha-b7872b8-x86_64.appimage build, there is severe lag when dragging the bounding box of a vector line/shape. This also happens with other recent 4.3.0-prealpha appimages.

STEPS TO REPRODUCE
1. Draw a vector line/shape, select it with the Select Shapes tool
2. Grab and drag one of the handles on the bounding box.

OBSERVED RESULT
It takes up to 5 seconds for the bounding box to respond to the cursor movement and then a little more time for the line/shape to follow the change.

EXPECTED RESULT
The bounding box should follow the cursor with no lag and the line/shape should follow with very little lag as it does in 4.2.5 and previous versions.

SOFTWARE/OS VERSIONS
Krita

 Version: 4.3.0-prealpha (git b7872b8)
 Languages: en_GB, en
 Hidpi: true

Qt

  Version (compiled): 5.12.4
  Version (loaded): 5.12.4

OS Information

  Build ABI: x86_64-little_endian-lp64
  Build CPU: x86_64
  CPU: x86_64
  Kernel Type: linux
  Kernel Version: 4.19.0-5-amd64
  Pretty Productname: Debian GNU/Linux 10 (buster)
  Product Type: debian
  Product Version: 10

Hardware Information

  GPU Acceleration: auto
  Memory: 16039 Mb
  Number of Cores: 8
  Swap Location: /tmp

ADDITIONAL INFORMATION
GPU acceleration and Instant Preview seem to have no effect on this.
If the handle drag follows a slow complicated path, the lag is greater.
During the drag and slow response, the CPU activity is much greater than it is than when doing this with version 4.2.5.