Cannot access LG NAS drives via afp using OSX 10.7.5 but can access them via smb

We have two NAS N1T3 drives on our home network. For some unknown reason, we suddenly can't access them via afp / bonjour as we have always done before, from any of our networked MACs. We can still access them via 'connect to server' within finder and using smb pre-fixes to their location. Both of these setups will mount the first NAS; smb://LG-NAS-1 or smb://192.168.0.18 or the second NAS (with just different addresses). We can then use them as normal, which is handy as we have lots of shared stuff on them!

if we try the normal Bonjour attempt within Finder via the 'shared' links (as we have always been able to do before) we get nothing apart from an eventual timed out error message on both of the NAS.

The specific details are:

LG NAS N1T3 Drives, with active afp, nfs and samba support. They are not UPnP enabled and neither is our router (this has always been the case). They both have static ip addresses which haven't changed at all. We are trying to connect with iMacs and Mac Book Pros all on OSX 10.7.5.

If we use Windows laptops or Ubuntu laptops on the network, they can all detect and connect both the NAS drives straight away.

If we use apps within any of our iPhones or iPads, we can also connect and see the drive contents straight away.

Time Machine works perfectly on all the iMacs and Mac Book Pros all on OSX 10.7.5 via afp / Bonjour.

The only thing that has changed very recently as far as I can remember, is an update to Safari, but I can't see that being important or connected at all.

I've searched on here in advance of this post but can't see the same set of circumstances, but any guidance / clues would be really helpful.