To put the risk into context: You get higher pericardial inflammation risk from tattoo, piercing the ears or going to dentist. The inflammation risk level is close to what you get from getting your skin pierced with supposedly sterile object.
Occurrences of hypersensitivity and inappropriate immune responses to vaccines are inevitable if the vaccine tries to boost immune system. The risk is higher with young people because they have more active immune system.
With one order of magnitude lower risk you almost certainly will get even worse, like Guillain-Barré syndrome (GBS). That happens with normal flu shots as well. Just the genetic variation among people makes it almost certain that 1 in 1,000,000 gets fucked.
ps. The risk of myocarditis (or pericarditis or myopericarditis) from primary COVID19 infection among young males infected with the virus is up 6 times more likely s as those who have received the vaccine. https://pubmed.ncbi.nlm.nih.gov/34341797/