Some (very) old mods still use "Modifiers" as a field, rather than the modern "Attributes". These are largely synonymous, but dynamic inventories do not read the old way of giving tags. To test, make two missiles with the same tags, but one using the old and one the current way of defining them. Look at stations with dynamic missile stocking: only the modern one will be stocked.
...this can either be fixed by ignoring it, breaking it further so that old code is obvious and pops an error code(this is a bug that's very hard to spot potentially), or adding in extra compatibility code.