I am having the same issue!
I have added the weights to all my products for my entire store.
Every now and then a product reverts back to 0 weight.
I can't figure out what the common denominator is for the issue. It can happen if I do or don't edit a product description, add a tag, do nothing at all.
All seems very random.
Has anyone else had this issue and know how I can prevent it in the future?
Thanks in advance for any help guys