SUMMARY
When trying to open a file or creating a new one krita  takes many seconds (more than 14 seconds)  to actually load the canvas be it a kra or a png file , in most cases it stops responding while doing this operation.  Once the canvas is loaded, if I close it and try to click the new file or open file buttons in the welcome page it will not show any indication it was clicked and take around 14 seconds again for the dialogs to appear. 

I tested with many versions and seems to be happening since beta 3, and the problem still persists on beta 5 most recently nightly (all versions tested listed ahead). In beta 2 the loading times were much shorter and the program was still responsive.

Tested with canvas 3000x3000 size, 8bit depth and 300 ppi

Logs down below



STEPS TO REPRODUCE
1.  click the new file or the open file button
2.  create a new canvas or open an existing canvas

For the other part of the scenario
1. close the canvas
2. click the new file or the open file button

OBSERVED RESULT
Canvas taking too long to load

EXPECTED RESULT
canvas loading in less time


SOFTWARE/OS VERSIONS
Windows:  Windows 10

TESTED WITH VERSIONS
krita-nightly-x64-5.0.0-beta5-0e4b8448bf
krita-x64-5.0.0-beta5
krita-nightly-x64-5.0.0-beta5-0e4b8448bf
krita-x64-5.0.0-beta3

Logs
SESSION: 15 Dec 2021 20:18:45 -0300. Executing K:\KritaStuff\Portable\krita-nightly-x64-5.0.0-beta5-0e4b8448bf\krita-nightly-x64-5.0.0-beta5-0e4b8448bf\bin\krita.exe

Krita Version: 5.0.0-beta5 (git 0e4b844), Qt version compiled: 5.12.12, loaded: 5.12.12. Process ID: 17888
-- -- -- -- -- -- -- --
15 Dec 2021 20:18:45 -0300: Style: fusion. Available styles: windowsvista, Windows, Fusion
15 Dec 2021 20:19:07 -0300: SAFE ASSERT (krita): "result.size() == 1" in file C:\Packaging\workspace\Krita_Stable_Windows_Build\krita\libs\resources\KisStoragePlugin.cpp, line 92
15 Dec 2021 20:19:07 -0300: SAFE ASSERT (krita): "result.size() == 1" in file C:\Packaging\workspace\Krita_Stable_Windows_Build\krita\libs\resources\KisStoragePlugin.cpp, line 92
15 Dec 2021 20:19:07 -0300: SAFE ASSERT (krita): "result.size() == 1" in file C:\Packaging\workspace\Krita_Stable_Windows_Build\krita\libs\resources\KisStoragePlugin.cpp, line 92
15 Dec 2021 20:19:07 -0300: SAFE ASSERT (krita): "result.size() == 1" in file C:\Packaging\workspace\Krita_Stable_Windows_Build\krita\libs\resources\KisStoragePlugin.cpp, line 92
15 Dec 2021 20:19:07 -0300: SAFE ASSERT (krita): "result.size() == 1" in file C:\Packaging\workspace\Krita_Stable_Windows_Build\krita\libs\resources\KisStoragePlugin.cpp, line 92
15 Dec 2021 20:19:07 -0300: SAFE ASSERT (krita): "result.size() == 1" in file C:\Packaging\workspace\Krita_Stable_Windows_Build\krita\libs\resources\KisStoragePlugin.cpp, line 92
15 Dec 2021 20:19:07 -0300: SAFE ASSERT (krita): "result.size() == 1" in file C:\Packaging\workspace\Krita_Stable_Windows_Build\krita\libs\resources\KisStoragePlugin.cpp, line 92
15 Dec 2021 20:19:07 -0300: SAFE ASSERT (krita): "result.size() == 1" in file C:\Packaging\workspace\Krita_Stable_Windows_Build\krita\libs\resources\KisStoragePlugin.cpp, line 92
15 Dec 2021 20:19:07 -0300: SAFE ASSERT (krita): "result.size() == 1" in file C:\Packaging\workspace\Krita_Stable_Windows_Build\krita\libs\resources\KisStoragePlugin.cpp, line 92
15 Dec 2021 20:19:07 -0300: SAFE ASSERT (krita): "result.size() == 1" in file C:\Packaging\workspace\Krita_Stable_Windows_Build\krita\libs\resources\KisStoragePlugin.cpp, line 92
15 Dec 2021 20:19:07 -0300: SAFE ASSERT (krita): "result.size() == 1" in file C:\Packaging\workspace\Krita_Stable_Windows_Build\krita\libs\resources\KisStoragePlugin.cpp, line 92
15 Dec 2021 20:19:07 -0300: SAFE ASSERT (krita): "result.size() == 1" in file C:\Packaging\workspace\Krita_Stable_Windows_Build\krita\libs\resources\KisStoragePlugin.cpp, line 92
15 Dec 2021 20:19:07 -0300: SAFE ASSERT (krita): "result.size() == 1" in file C:\Packaging\workspace\Krita_Stable_Windows_Build\krita\libs\resources\KisStoragePlugin.cpp, line 92
15 Dec 2021 20:19:07 -0300: SAFE ASSERT (krita): "result.size() == 1" in file C:\Packaging\workspace\Krita_Stable_Windows_Build\krita\libs\resources\KisStoragePlugin.cpp, line 92
15 Dec 2021 20:19:08 -0300: SAFE ASSERT (krita): "result.size() == 1" in file C:\Packaging\workspace\Krita_Stable_Windows_Build\krita\libs\resources\KisStoragePlugin.cpp, line 92
15 Dec 2021 20:20:06 -0300: Non-store package - creating updater
15 Dec 2021 20:20:35 -0300: Created image "Unnamed", 3000 * 3000 pixels, 300 dpi. Color model: 8-bit integer/channel RGB/Alpha (sRGB IEC61966-2.1). Layers: 2
15 Dec 2021 20:21:52 -0300: Importing image/png to application/x-krita. Location: F:/Larissa/Pictures/Desenhos-2019.04/Monstros/cave gremelin.png. Real location: F:/Larissa/Pictures/Desenhos-2019.04/Monstros/cave gremelin.png. Batchmode: 0
15 Dec 2021 20:21:52 -0300: Loaded image from image/png. Size: 2180 * 2216 pixels, 4.16665 dpi. Color model: 8-bit integer/channel RGB/Alpha (sRGB built-in). Layers: 2
15 Dec 2021 20:22:20 -0300: Importing application/x-krita to application/x-krita. Location: F:/Larissa/Pictures/Desenhos-2019.04/Monstros/cave gremelin.kra. Real location: F:/Larissa/Pictures/Desenhos-2019.04/Monstros/cave gremelin.kra. Batchmode: 0
15 Dec 2021 20:22:20 -0300: Loaded image from application/x-krita. Size: 2180 * 2216 pixels, 4.16667 dpi. Color model: 8-bit integer/channel RGB/Alpha (sRGB IEC61966-2.1). Layers: 5