did you check the dates on the bags of feed?
There are too many experienced keepers, including people who have not signed up to conspiracy theories about it, and people whose posts in the past have led me to believe what they say and think they are not idiots, reporting suspicions with their feed. And if you look, there are similar threads from years ago, long before all the nonsense started.
There are also a lot of inconsistencies when the 'data' (info) is aggregated under a product name (as if all examples of that product, or manufacturer, or brand were involved), leading sensible people to dismiss it as internet nonsense or inexplicable. A (to me) plausible explanation for the reported phenomena is people have inadvertently and unknowingly bought bags of feed that are so old the nutrients are more or less short of what they were when the bag was packed, and the formulations aim for the minimum required, so any loss from there matters. It appears that feedstore and warehouse staff are not always as careful about stock rotation as they should be, or do not themselves understand the codes used on the feed bags to indicate when they were made.
I hypothesize that those having no issues have been getting fresh feed. Those having issues might want to have a look at the milling date on their suspect feed, if they still have it, or what they've got in store if they buy in bulk but don't use in bulk. If there are a lot of recent dates, that would refute this idea.
I'm not sure what is causing our issue, but it's definitely not old feed. Our local area has robust livestock needs and quick feed turnover. Some of the feed stores around here would more likely run out of feed than have to sell old stock.