This issue has been resolved. RingCentral released a downloadable update via the App Store to fix the problem.
Some iOS users who have previously updated their RingCentral mobile app to 7.5 have reported the app keeps crashing everytime they launch it. This is a very specific case and currently affects only a few customers. The crash affects users whose iOS-stored Contact phone numbers contain non-numeric characters.
To fix the issue, update your RingCentral mobile app to the latest version, 7.5.1. For the instructions, check Installing the RingCentral mobile app via iOS.
A saved phone number in their personal iPhone/iPad contacts contains an invalid non-numeric character. The previous mobile app (7.5.0) version's code could not handle non-numeric characters smoothly. It could not translate the non-numeric characters to numbers, thus the app crashes when launched.
Here were some temporary fixes:
1. Disable permission for RingCentral mobile app to read native iOS contacts.
On your iPhone/iPad, tap Settings.
Scroll down, then tap Privacy.
Tap the slider button across RingCentral to disable this setting.
NOTE: You can enable this setting once the fix has been released.
2. Edit and correct the contact number.
Search through your iPhone/iPad's contact list and edit the affected contact number/s. Ideallly, your contacts' saved phone number should not have any non-numeric character. Once this is corrected, the RingCentral mobile app should launch without any problems.
Checking the Latest Feature of the Mobile App
RingCentral Mobile App for iOS Overview
RingCentral Mobile App Frequently Asked Questions