How .prproj and .aep differ
Both are Adobe project files, but one is a cutting format and the other a compositing format, with different internal structures and different version rules. That is why this site ships two separate downgraders.
What each one holds
A .prproj is a Premiere Pro project: it describes an edit — sequences, tracks, media references, transitions and basic grading. A .aep is an After Effects project: it describes comps — layers, effect chains, expressions and render order.
Why they are not downgraded the same way
The two record different structures and have different needs. The Premiere line can run on a server because an edit structure is separable from its media. After Effects projects are heavy and depend on the render environment, so handling them locally in the browser suits them better — the two lines were always going to work differently.
Dynamic Link and versions
Dynamic Link pulls an AE comp straight into a Premiere timeline and appears to skip exporting. It is sensitive to versions: both sides must match, and upgrading or downgrading either end can break it. When versions diverge, rendering the comp to an intermediate file is the steadier route.
Practical advice for handovers
If a job uses both editing and compositing, align versions on both sides. Do the .aep first, then bring the .prproj down to the same era, so you never end up with an edit that opens while its linked comps do not.