Your corps will only employ the LOWEST percentage type worker that is available.
For instance, if you have 6x as many high level managers as you need, but only 75% of the number of low level managers, then only 75% of the required high level managers will be hired, even though you have more than enough to fill all high level positions.
If you go to your education screen it should show you how many are available of each type and how many are needed for full capacity. If, in any row, the number needed for 100% production exceeds the available workers, then you need to educate more of that professional type.
I took a glance are your corps page. First of all good job on such a high level of employee welfare! But yea, the hiring loss doesnt seem to be concentrated...so im thinking your probably just understaffed on one type of worker (probably high level, always happens to me).
Hope this helps.