Why can’t I connect to a specific Wi-Fi router?

The Android security tools that limit apps’ access to device IMEI, serial number, and other identifying information. It will also give you a little more protection when using Wi-Fi networks by randomizing your device’s MAC (media access control) address.
If you use your device for business, your organization might require Wi-Fi mac address of your device for wireless connection. Privacy setting of Wi-Fi use randomized MAC by default, you need to change it to “Use device MAC” manually, follow steps below to change:
1) Touch “Settings”
2) Touch “Wi-Fi”
3) Touch and hold the Wi-Fi name with connected status in the list
4) Touch “Modify” in the dialog that opens
5) Touch “Advanced options”
6) Touch “Use randomized MAC” under privacy, then touch “Use device MAC” in the pop-up menu.