Unable to reproduce WebKitLegacy -[_WebSafeForwarder forwardInvocation:] crash

I have the same issue, I used [NSAttributedString alloc] initWithData to load the HTML string on a label. My crashes often happened when the app switch between Background mode and Foreground mode. I got some tips from Apple's documentation, I think this might be useful.

Following are the discussion on Apple's NSAttributedstring doc：

The HTML importer should not be called from a background thread (that is, the options dictionary includes NSDocumentTypeDocumentAttribute with a value of NSHTMLTextDocumentType). It will try to synchronize with the main thread, fail, and time out. Calling it from the main thread works (but can still time out if the HTML contains references to external resources, which should be avoided at all costs). The HTML import mechanism is meant for implementing something like markdown (that is, text styles, colors, and so on), not for general HTML import.