I occasionally have this problem. I gently mist water onto the helmet, put a misted dome over it to raise humidity and in a few hours they pop off on their own. My problem was caused by low humidity seemed to dry up quickly after breaking soil.
You can also plant it with the tap root sticking up, I always just plant the seed with the pointy part up. I don't remember the exact science, but it helps get the husk off.
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Are you sure your getting fresh seeds or seeds that have been stored correct. Old seeds or seeds increctly stored will dry out over time and get weaker. You end up with seeds were the iner sack becomes to dry and tough so its dificult to shake off or they no longer have enough energy to completly shake them off. Or the outer shell becomes so dried and hard that they no longer have the energy to crack them. Happens alot with old or incorrectly stored seed. If it happenes alot ie more than 50-60% something is defo up . Its always good to know how old the seeds are and if theyve been stored properly. Or is is the area your keeping them in very dry
