I’m afraid our team isn’t aware of or investigating any issues with subgraph performance in OmniGraffle 7.11+ yet, so if you’d be willing to contact us directly with more information about the issue, we’d love to investigate this further so we can try to fix this.
Please use Help > Contact Omni, or email our support team directly at firstname.lastname@example.org with more information about the problem so we can try to look into this. If this is your first time reporting a bug, please follow the recommendations listed here.
After clicking Contact Omni, you can share a redacted version of the file by checking the box before clicking Include Document.
I’m glad you’ve been able to work around this for the time being by reverting to an earlier build, but it’s not going to be a great long-term solution for you to remain indefinitely on an older version of the app, so hopefully we can collect the information we need to provide a fix for this in the future. The forums are a great place for community discussion, but our team only checks in periodically between our other responsibilities, so if you’re having a problem with our software, the best way for us to investigate issues or provide technical assistance would be over email.