ID 427120 - Importing Udims into Mari 4 is noticeably slower than Mari 3

Problem summary
Importing Udims into Mari 4 is noticeably slower than Mari 3.

Customer reported version
Mari 4.6v1

Customer reported platform
CentOS 7

Steps to reproduce

1) Create and configure a Channel with the same resolution and colorspace config as your source images.

2) Go into the Layers palette and select the default single paintable layer.

3) Right click > Import into Current Layer.

4) Ensure you choose the same colorspace from the dialog that allows you to navigate to the source sequence.

Expected behaviour
Mari 4 shouldn't be significantly slower to import Udims than Mari 3.

Actual behaviour
Mari 4 shouldn't be significantly slower to import Udims than Mari 3.

Workaround
Unknown.

Reproduced by support
Mari 4.6v3 - Windows 10 - CentOS 7 

Mari 4.0v1 - Windows 10 - CentOS 7 - Regression

Earliest version tested
Mari 4.0v1 - Importing Udims into Mari 3.4v4 is noticeably faster so has regressed.