I started multiple gameplays and played all to around 1500, one to 1550. I discovered that in ALL and ONLY Provinces of the HRE + the Province of Venice, the Nobles and Clergy constantly emmigrate. It didnt depend on the needs, that are fullfiled, either the academic size and investements. No matter what, they continue to emmigrate and because of that ther is a permant disgrowth on them. It is strange that this happens only in HRE Provinces.