Getting unknown error about "dynamic accessors failing" after updating to macOS : <p>After upgrading to macOS Sierra (10.12) and Xcode 8.0 (8A218a), I began getting many error messages in my macOS/Cocoa app (written in Objective-C) that follow this format:</p>

<pre><code>[error] warning: dynamic accessors failed to find @property implementation for 'uniqueId' for entity ABCDInfo while resolving selector 'uniqueId' on class 'ABCDInfo'.  Did you remember to declare it @dynamic or @synthesized in the @implementation ?

[error] warning: dynamic accessors failed to find @property implementation for 'uniqueId' for entity ABCDContact while resolving selector 'uniqueId' on class 'ABCDContact'.  Did you remember to declare it @dynamic or @synthesized in the @implementation ?

[error] warning: dynamic accessors failed to find @property implementation for 'uniqueId' for entity ABCDEmailAddress while resolving selector 'uniqueId' on class 'ABCDEmailAddress'.  Did you remember to declare it @dynamic or @synthesized in the @implementation ?

[error] warning: dynamic accessors failed to find @property implementation for 'address' for entity ABCDEmailAddress while resolving selector 'address' on class 'ABCDEmailAddress'.  Did you remember to declare it @dynamic or @synthesized in the @implementation ?
</code></pre>

<p>None of this is my code or code from 3rd party developer libraries that I'm using, and doing a search on those variable names (i.e: 'uniqueId' or 'ABCDInfo') does not pull anything up, indicating it's not in my project.</p>

<p>I saw that this issue was also reported on Apple's Developer Forums twice (<a href="https://forums.developer.apple.com/thread/64189">Issue 1</a> and <a href="https://forums.developer.apple.com/thread/64274">Issue 2</a>), but both questions remain unanswered   </p>

<p>My question is: What causes these error messages and how can I fix them? 
It doesn't cause my app to crash, but I'd rather figure out and understand what's wrong.</p>
