This looks like a low memory crash for two reasons:
- You and Shadow Wizard are seeing crashes, I'm not getting crash reports, and apparently Crashlytics can't tell me about low memory crashes. 😞
I just profiled looking at the question and saw this:
The editor text view is ordering up a ridiculous amount of memory in order to even get you started. Memory usage jumps up by about 240MB rendering that monster occasionally form a steady state of ~300MB to 420MB on certain changes. It is possible that we can get that down some if we drastically restructure the editor but I think the answer is that the editor doesn't support excessively long text.
Not sure what the remedy should be since we don't know what reasonable cutoffs are for each device. My 6 for example was slow but able to make some changes and render a preview. A 6+ might not be because of the increased screen density, a 4S might not be because of less available memory with a roughly equal drawing area.