normal but also "not so normal" - the smell is related to decomposition of the initial sodium thiosulfate (& misc) solution, releasing the distinctive smelling S (sulfur or "rotten egg" smell)
eg,
Na2S2O3 --> 2Na + SO3 + S
For aquarium use, stabilizers are added, also various other components (such as EDTA etc to bind heavy metals) & various proprietary compounds (depending on how many magical reactions are attributed to the water conditioner) ... upon initial production, there is usually a faint S odor, over time this may increase - if solution actually looks yellow (& about knocks you over) there's not much intact sodium thiosulfate remaining to react with the chlorine in your tap water.
If you read the fine print, the manufacturer should provide an estimate of how much solution reacts/neutralizes how much chlorine (in tap water),
eg, Prime states
Use 1 capful (5 mL) for each 200 L (50 gallons*) of new water. This removes approximately 1 mg/L ammonia, 4 mg/L chloramine, or 5 mg/L chlorine.
if there is significant decomposition then this amount of chlorine etc neutralized will decrease (possibly a lot), so you can double dose & hope that covers it, or return "smelly" product for new & so on ...
If your water supplier uses chloramine rather than chlorine, your livestock will appreciate water conditioner that is properly stabilized & stored.
(check manufacture & expiry dates on bottles, store in a cool, dim (dark) place, once opened use bottles within a reasonable time period; if you buy in bulk, then consider dispensing into smaller bottles which are kept full & closed while being stored)