Kaspersky Who Calls has the following known issues on different devices:
On devices running Android 5.1 and lower with two or more SIM cards the app may not identify incoming calls on one of the SIM cards. This is caused by technical issues on Android 5.1 and lower.
Kaspersky Who Calls does not block incoming spam calls on the second line.
On devices running Android 8 the app may not block incoming calls.
Kaspersky Who Calls does not check or block some non-standard numbers that are not associated with any country’s national telephone numbering plan or the IP telephony operators’ plans.