"Loading Resource Packs" taking a long time when joining

As with a previous resolved ticket, some of my friends are having a problem when joining the Realm whereby it takes an incredibly long time to pass the "Loading Resource Packs" stage of entry, sometimes not progressing beyond this at all before they back out and try again.

 

We have only got the Default Texture and Behaviour packs running so I cannot understand why this takes so long. Is it a bug of some form and if so, is there a way of fixing it?