Starting in iOS 11 there are checks that UI operations are called in the main thread. Some CleverTap calls are being reported e.g.
Main Thread Checker: UI API called on a background thread: -[UIApplication keyWindow]
PID: 12544, TID: 710282, Thread name: (none), Queue name: com.apple.root.default-qos, QoS: 21
4 LostTest 0x0000000102c6d254 -[CleverTapAPI currentViewController] + 64
5 LostTest 0x0000000102c6d2e4 -[CleverTapAPI checkCurrentViewController] + 32
This doesn't appear to cause a crash but I have had a crash from another part of code doing the same so maybe worth fixing in next library update