I have submitted app and got rejected for an issue which I am not getting when I install my app on development store. I have created an app in PHP but got rejected due to error occurred at a time of installation. However, I am not getting that issue when I install that app in development store. Here's a requested change:
We were redirected to an error page when attempting to install your app. Please test your app's installation on a development store using OAuth before resubmitting. Please see this screenshot for additional details.
So did you see anything in your logs? There was most likely a problem on the server side causing a 500 or something?
The only thing you can do in this case is check and double check the code you have. It is most likely a step you are missing (for example, I had the same problem as you - could not reproduce the issue that Shopify QA was indicating - and I was in denial. I'll be quite honest with you about that. I was convinced that it was a bug in a Shopify or Koa library and nothing to do with me. In further examination, some frustration, I found it WAS a 'me' problem.
The difficulty in not being able to reproduce the issue is a problem, but this is what will set your sleuthing and development skills apart from the 'others'. The ability to figure it out in the end.... hang in there. You won't get additional information from Shopify on this. I can suggest:
1 - In your local development environment, add logging to the n-th degree.
2- Double check / read / triple check the Shopify documentation (which isn't always easy to understand) and keep looking at it until you figure out what you've missed.
3- Raise a ticket with Shopify indicating you couldn't repro the problem, then resubmit quoting the ticket number in your submission. Track in the ticket so that the QA knows what's going on. This way will help you not get penalised if you resubmit several times and it still doesn't work.
Most likely it's a you problem (sorry to say). Most likely it's to do with Auth. Perhaps not verifying every request (this was my problem) so header's weren't being set correctly, etc etc.
Hope this helps a little bit.