Background build and VS2019 freeze on open solution

Described problems appear after update VS to 16.9.2 from 16.4.3 and qt vs tools to 2.7.1 from 2.4.3.
Solution has many qt projects(50+) one "exe", others are class libraries. When open solution after VS start Qt VS Tools after initial initialization in output window logs:

xxx.vcxproj: background build FAILED!
yyy.vcxproj: background build FAILED!

 But for some projects it has not one entry but 6-8:

zzz.vcxproj: background build FAILED!
zzz.vcxproj: background build FAILED!
zzz.vcxproj: background build FAILED!
zzz.vcxproj: background build FAILED!
zzz.vcxproj: background build FAILED!
zzz.vcxproj: background build FAILED!

In this moment VS freezes, not respond and memory consumption grows from 1100 Mb without qt vs tools to 2500+Mb. It may last for several minutes, and since VS is x86 app it may lead to crush with System.OutOfMemoryException, then VS restarts and qt vs tools does not start any background builds(or seems so) and you can use VS.
Similar behaviour appears when you reopen solution or reload batch of projects from it, or even when you simply surf projects/files in solution.
And also it can lead to VS crush on rebuild solution with also OOM exception, but it's not confirmed.