When the server tells the client to download a resource pack, the client can halt for a very long period of time. On slow computers the player will timeout and have their minecraft freeze for many minutes if they are on low-end hardware. 

Here is a snippet from my log:

[01:13:53] [Netty Client IO #2/INFO]: Found file ~~~~\server-resource-packs\6273aac1dcacc7098d02a3f03a8deef67f3dd0dc without verification hash
[01:13:53] [Client thread/INFO]: Reloading ResourceManager: Default, 6273aac1dcacc7098d02a3f03a8deef67f3dd0dc
[01:14:00] [Client thread/INFO]: SoundSystem shutting down...

You can see that it took over 7 seconds to reload the resource pack. (This pack is empty and is used to clear the players resource pack but packs with content cause issues as well!)

Some of my players are reporting up to minutes at a time so please fix this.

EDIT: Critical info I noticed, if you connect with the direct IP address to the server there is no problem. If you use a domain name then it can take a very long time.