LR not recognising my lenses

I wonder is someone could offer the reason why my LR no longer recognises two of my lenses. I have the following;

Nikon 24mm f2.8D
Nikon 16 - 35mm f4 G
Sigma 70 - 300mm f4 DG

I use these lenses on a Nikon D750 body.

I started using LR just a few months ago and up until last weekend LR recognised all three lenses. Sunday I suddenly noticed that it no longer recognised the Sigma. In fact I cannot even manually select the sigma. According to LR is doesn't exist. This morning I used the 16 - 35mm and noticed LR doesn't recognise this one either although it still recognises the 24mm. prime. No updates have been applied in the last week or so!