I'm active in this topic and have never heard anything similar to what you've mentioned. And in looking this up, there's a very recent study [1] that's quite relevant. They studied the cardiovascular health of astronauts for 5 years after their return from long-duration stays on the ISS. They were all perfectly healthy.

[1] - https://journals.physiology.org/doi/full/10.1152/japplphysio...