Events with identical stacktraces not being grouped


I have 2 errors (including urls in case sentry admins can investigate):

Am using sourcemaps and both have identical stack traces:

TypeError: Cannot read property 'offsetTop' of undefined
  at call(pwa/routes/search/browse/digitals/contracts.js:158:1)
  at invoke(backburner.js:227:1)
  at flush(backburner.js:134:1)
  at flush(backburner.js:290:1)
  at end(backburner.js:423:1)
  at _runExpiredTimers(backburner.js:880:1)
  at apply(backburner.js:381:1)
  at wrapped(vendor/raven.js:428:1)

But they are not grouped.

Since, according to: “If a stacktrace or exception is involved in a report, then grouping will only consider this information.”, I would expect these 2 errors to be grouped, since they have the same stack trace.

Do you know why those 2 errors aren’t grouped? Do you have any tips for how to get sentry to group these errors?