Maybe the milestone reordering feature could be behind an opt-in toggle? Personally I don't see any problem with that and I'm also not sure why milestones have to be strictly sequential in the first place. I found myself creating milestones accidentally out of sequence and the only way to "reorder" was renaming the milestones, which felt quite punishing.

In T15105#3239, @Matthew wrote:

In T15105#3233, @tiguchi wrote:

As a bandaid I patched the extractFilePHIDs method in PholioImageFileTransaction.php by adding a nested foreach loop as follows:

foreach ($new_phids as $phids) {
  foreach ($phids as $phid) {
    $file_phids[] = $editor->loadPholioImage($object, $phid)
      ->getFilePHID();
  }
}

This fixes the problem on our installation for now, but I would like to avoid having to manage any local changes

Would you be willing to create a revision so we can put that fix into upstream? If you're not sure how, or need some help, feel free to ping me!

Small update: I just migrated our Phabricator installation to Phorge following the instructions in Update From Phabricator. The migration worked, but we still cannot upload new mockups.