Hi metbag,
We have not come across any known issues with the WiFi cards in Inspiron 3521, as it ships with Dell Wireless 1703 and 1704 WiFi/Bluetooth 4.0 combo card. The card replaced by is an older model and thank you for the information provided. However, updating the wireless drivers and the system BIOS would fix the WiFi issues. The latest drivers and BIOS can be downloading from the following link by punching in the Service Tag and by clicking on the Drivers & Downloads tab:
http://dell.to/117d6Zu
Please let me know if you need further information.