A little more information might be needed such as which device you are using. Perhaps submit a formal bug report so that the developers have a little more information to work with.
Opera Mini is working fine here on both an iPhone SE and 6S Plus which both updated to iOS 11 without any noticeable problems.
iPad Mini 2
Both worked fine before update.
Cause of Crash: The developers did not update the app to 64-Bit Architecture, which is NOW REQUIRED IN APPLE PRODUCTS as 32-Bit was dropped in this update.