The one main reason for F1 variation is mutation.

Aminu Moriki Ladan

How old are those F1 seeds? Where are they stored? Older seeds tend to lose different degree of germination vigor.

Dear Aminu Moriki Ladan it depends of the number of parents involved in mating and their genotype. If either female and male parents are clones, F1 should be genetically uniform, at least external factors occur (mutations, contamination,...). However, if parents aren't clones, variations must be expected.