ID 318140 - Adding a new layer to an archive containing 1000 UDIMs takes considerably longer in 3.3v1

Problem summary
Adding a new layer to an archive containing 1000 UDIMs takes considerably longer than it did prior to 3.3v1

Customer reported version
3.3v1
Customer reported platform
ubuntu

Steps to reproduce

1) Create a new archive using the attached object (1000_UDIM.obj) or use the attached user archive

2) Launch archive and create a channel

3) Create a layer

4) Observe that layer creation consistently takes over 1 minute to create. In 3.2v1, this is a matter of seconds.

Additional tests:

5) Using [CTRL+S] to save the archive; observe that performance is also affected

6) Attempt to export the layer from the archive; observe performance is affected.

Log attached.

Workaround
Unknown.

Reproduced by support
This bug has been reproduced in:
Mari 3.3v1 - Windows 7, CentOS 6.8
Unable to reproduce bug in:
Mari 3.3v1 - OSX 10.12.4
Mari 3.2v1 - Windows 7, OSX 10.12.4, CentOS 6.8

Earliest version tested
Last working version: 3.2v1

Expected behaviour
Creating a new layer, and all other methods tested, should react quickly. The project should be quick to open, save and create a layer or channel.

Actual behaviour
All tested methods were significantly slower in 3.3v1 than in 3.2v1. For example, when tested, creating a new layer in 3.3v1 consistently took roughly a minute to create whereas it took around 3-5 seconds in 3.2v1.