Trying to do everything at once
The current application tried to do everything at once. All tools (scanner, listview with art, etc.) and information were cramped inside the same 375*812px view of the installers's iPhones. Custom scroll views tried to solve this but only made it worse.
Creating cognitive overload
Instead of only showing the needed information, the app tried to show too much (unnecessary) information at once. This resulted in a UI that missed focus, created a lot of cognitive overload, and required a lot of unnecessary scrolling.
A sense of spatial confusion
There was no relationship between the job to be done and the way you navigated from one view to another (different types of buttons, modal views versus page views, etc). The lack of hierarchy created a sense of spatial confusion.
No consistent visual language
Branding matters less in internal business tools, but using the same styling to indicate certain types of actions or statuses could help the installers to not have to think about using the product, focus on their work, and make fewer mistakes.
A lot of other issues
There were a lot of small other issues, like setting a digital signature that just didn't work seamlessly.