To the best of my knowledge, the fact that thrombosis is a (rare) side effect of Astra Zeneca and Johnson is pretty thoroughly established. It's a pretty specific type of thrombosis, and afaik it doesn't occur eg. for the Biontech and Moderna vaccines.

I know there's a lot of misinformation about the vaccines going the rounds, but that doesn't mean that all reports of side effects are made up or statistical noise.