Back around 1968-1969, SCIENCE AND MECHANICS magazine has a series of articles claiming the Gagarin’s trip into space was a fake. They also claimed later trips into space were also fakes.
Now that you mention it, I remember something about Gagarin being ejected at 20,000ft, technically making him ineligible for a “first” record of a successful takeoff and landing.
The Soviets weren’t too sure about landing survivability at the time.