Reimport of one Material or .txt file when big scene is opened takes twice more time in 2021.2.beta than in 2021.1.f

Import time for empty .txt file when scene with 100 000 GameObjects is opened:
280.000 ms in 2021.1.6f1 -> 250.000 ms in 2021.1.25f1, 2021.2.0a9 -> 500.000ms in 2021.2.0b2 -> 450.000ms in 2021.2.0b15 -> 450.000ms in 2022.1.0a12

How can we reproduce it
1 Open any "big" project and open a "big" scene in 2020.3.f or 2021.1.f
2 Create a .txt file in the root of Assets folder
3 Select that .txt in Project Browser and RightMouseClick->Reimport a few times in a row
4 Open Editor.log and see how long it took to perform Reimport

5 Open the same "big" project and the same scene in 2021.2.b or 2022.1.a
6 Select .txt again in Project Browser and RightMouseClick->Reimport a few times in a row
7 Open Editor.log and see how long it took to perform Reimport
8 Compare import times from steps 4 and 7

Actual results: import takes twice more time in 2021.2.beta than in 2021.1.f

Expected results: ideally import times should be the same