After mirroring a supported object the spheres at support branches can end up with inverted normals. If you don’t spot the error and print the supports can fail at the branches. Obviously the workaround is to flatten the supports before mirroring or resupport after mirroring however I have a file where spheres are inverted on both the mirrored and unmirrored part and I haven’t been able to figure out exactly how that happened.
e.g: this:
should look like this:
