In this case, we already have an extraordinarily rare occurrence. So your population isn't those observed to have the conditions "occurring 1–7 days post-vaccination," but individuals who've suffered SCD. I rather guess that anybody who died post injection didn't keep their appointment, either.
"The causes of SCD in athletes vary, with the estimated incidence of death between 1 in 40,000 to 1 in 80,000 persons"
"In athletes <35 years, inherited cardiac conditions such as hypertrophic cardiomyopathy and anomalous origin of a coronary artery are most common. "
Several passive surveillance systems reported increased risks of myocarditis or pericarditis, or both, after COVID-19 mRNA vaccination, especially in young men. We used active surveillance from large health-care databases to quantify and enable the ...
www.ncbi.nlm.nih.gov
If you rule out the conditions above, then I raise my bet.
Of course I don't belong to the cult of mRNA experimental genomic therapy, so I'd wager accordingly.