I edited my reply, but I see that notifications don’t always go out for those. So, I’m going to paste that edit here:
In the past, Photos did a really good job of converting Aperture adjustments (and rendering them faithfully and non-destructively). That has changed. I have run some tests with Mojave and Catalina beta and have found that, for the most part, Aperture adjustments are no longer converted. Instead, Aperture edits are generally treated as foreign data made by an external editor. In a few cases, Photos will convert the data (e.g., if there is only crop or a few other adjustments). In most cases, Photos simply creates (or reuses) a JPEG preview to represent the Aperture adjustments. Any further edits are made to the JPEG, not to the original (unless you revert to original). In some cases, the adjustment data is completely discarded, and you just get an unadjusted image. Whoa.
This is definitely a lot worse. On top of that, if you used a Photos on an older OS to convert (a version of Photos that did a better job), once you move to Mojave or Catalina, you get the new behavior. I’m still wrapping my head around what it all means, but I do know that it is really bad news for people, like me, hoping to move to finally move from Aperture to Photos.