Сталин и НКВД

As a result of the study, it turned out that in different republics and regions of the USSR in 1937-1938. there was no unified strategy of repression. In some regions, the leaders limited themselves to carrying out the orders of the center, in others they took the initiative, sometimes increasing the number of repressed people by 10-13 times. What is the reason why the repressions were carried out with varying degrees of intensity in different parts of the country? Apparently this is a consequence of the different positions of the regional leaders of the NKVD.
What, then, is the reason for the liquidation of the "Yezhov" leadership of the NKVD in late 1938 - early 1939? In the top leadership of the country, Stalin was supported by V. M. Molotov, L. M. Kaganovich, K. E. Voroshilov. It is their signatures, together with the signature of N. I. Yezhov, that are on the execution lists. What is the reason that only the "Stalin Commissar" was shot?
In order to find an answer to this question, the author tries to establish who led the local NKVD bodies in those regions where the repressions turned out to be the most bloody, what kind of relationship did these Chekists have with leaders of the People's Commissariat, which groups in the leadership of the NKVD they belonged to, what political goals they pursued.