This article applies to:
Skype for Business 2015 client
You constantly receive authentication pop-ups in you Skype for Business client.
This can happen if your computer has multiple active network connections. Typical example would be a laptop that is docked in a docking station and is therefore simultaneously connected to both Ethernet (wired) and Wi-Fi (wirelesses) connection. In an environment where the Wi-Fi signal is not very reliable, this can cause a connection flipping between the network connections. And since you are suddenly showing up to the server from another network with another IP address, the server will typically require you to re-authenticate, causing the login pop-up on you computer.
Disable the wirelesses connection when docked.
Most laptops also have an option in BIOS which can be set to automatically turn off the wirelles connection(s) when docked.
For example with Dell laptops you can find this option in BIOS under Power Management/Wirelles Radio Control. Turn on both Control WLAN and Control WWAN options.