Reason for files start showing reduced coverage?

[elenajdanova]

I was introducing minor changes in my code, additionally updating the tests.
I didn't add any tests, I didn't delete any tests.
Output is giving me drastically reduced coverage for several files, one of them wasn't touched at all in mentioned PR. Can somebody explain what's going on?

https://user-images.githubusercontent.com/16534638/162859122-be977572-5bef-4d46-92ff-c68d26f340e9.png

[ArtiomTr]

Answered in #265 (comment)