The "positive scram effect" was discovered at Ignalina (where the miniseries were filmed) in 1983. The RBMK design organization NIKIET sent an official informational letter to the power plants and proposed changes to the design and operational procedures. The changes weren't implemented as "there was a widespread view that the conditions under which the positive scram effect would be important would never occur." The same as O-rings.
And there was no "a Soviet program to fail Jewish students". Just primitive ground-level anti-semitism.