I can consistently repro this problem with Differential, and have (so far) found two different cases that repro this.
If I load the page for the revision (`/DXXXX`), all files load within a couple of seconds. However, if I use the "Show Diff" button in the "Revision Update History" section of the page to look at the delta between two diffs (ending up on a URL like `/DXXXX?vs=YYYY&id=ZZZZ&whitespace=ignore-all#toc`), then the following happens:
Most files load just fine, but several files stay stuck on "Loading..." indefinitely: {F362990}
By looking at the network tab of devtools, I can see that a request to `/differential/changeset/` 500s with the response:
```
>>> UNRECOVERABLE FATAL ERROR <<<
Maximum execution time of 30 seconds exceeded
/phab_path/libphutil/src/utils/utils.php:711
┻━┻ ︵ ¯\_(ツ)_/¯ ︵ ┻━┻
```
This also causes many JS errors, presumably because of the file that hasn't loaded:
```
Uncaught Error: JX.$('C2844557NL0') call matched no nodes.
```
Potentially helpful data: We're using git. In both the repro cases I found, the files that fail to load are >10k lines (whereas files that are <10k lines load fine). But again, these >10k line files load fine in the normal revision view -- it's only in the delta-between-two-diffs view that problems occur.
If you need any more info to debug or repro, let me know.