The apps do not update on the devices. This is a known issue with Microsoft and Apple. I've had support calls with engineers from both Apple and Microsoft on the call and the resulting solution was just ignore the errors in Intune. (endpoint.) My tenant is littered with hundreds of application install errors because the device will not or cannot get the app to update. Apparently it was because there is no user affinity on the device. If we wipe the iPad and re-enroll it will get the latest version of the app but we cannot force it to update the apps on the device and it just throws the error
An app update is available. Available apps can be updated using Company Portal and required apps will auto-update on device sync. 0x87D13B9F
Because Company Portal is not on devices without user affinity this cannot complete.
It's been an issue for 2 plus years or longer.