you gotta be careful when saving seed, there's two troubles you'll run into when replanting otherwise. most garden plants reproduce sexually, meaning they draw the genotype of the seed from two parents rather than from themselves. if your original pepper plant was a hybrid and you had other hybrids planted alongside, they'll breed with each other and the resulting phenotype isn't true to type because each successive plant selects genes against their parent randomly. additionally, if plants of the same species are planted close by you can have a similar issue with the seed's phenotype as other breeds of the same species will intermingle their genes with yours and cause a seed that doesn't grow true to type
in short if you continue to have harvest issues i highly recommend refreshing your seed stock and talking to neighbors to see if they're planting peppers close to you, as you may be sabotaging yourself. the tiny peppers do look cute tho