This issue is still occurring even after having reported it to Apple support and being in contact with someone from Apple support. (I provided them a Wifi Diagnostics report after issue occurred and with wifi debug/diagnostics setup)
The problem is strangely sporadic – some days it doesnt happen at all, other days it happens all the time and some days it’ll just occur once. Strangely enough, the higher the importance of the work I’m doing on the iMac, the more it occurs – well, the more I notice it – this leads to lots of ‘#!£%ing Apple!’ exclamations.
My latest attempt to try and get round this issue is by changing the Network Channel its using – it was on 11, now I’ve set it to 6. Lets see what happens…