A7ii camera unable to communicate with Sony lenses. Suggestions?

[Comberjohn]

Bought my second a7ii last January as used. In excellent condition with only just over 7000 activations. Has been working fine until today when, with just over 8000 activations now, it has started to play up. Took my first shot with a Sony 24-70 f4 attached with no issues using manual focus and then everything went blurred! Tried to switch back to AF on the Function menu but only had a grayed-out MF. Tried the OK and got the dreaded 'Invalid because lens not attached. Attach the lens correctly.'  

Thought it could be the lens and tried a virtually new Sony 50mm f1.8 that I had with me. Showed 'AF-S and f1.8 for about two seconds then the same. Tried it with a non electronic manual lens with no problems. When I arrived home I carefully cleaned all the concerned contacts on the camera and lenses. No difference. Both lenses are snug fit on the camera with no rotational movement so don't think its a mechanical issue.

Did a full camera reset. No difference. Software version is 4.01, so up to date.

I've contacted the seller to try and find out if it's still in warranty and if he still has the receipt before I send it to a repair centre. But no guarantees it's in warranty and if he has the receipt.

Any experience of similar or suggestions? I had sold my last a7ii and gone over to Fuji for a year but wanted to come back to Sony. Now, after a couple of months I'm not so sure...