Finally solved!!!
The issue is because the Mac mini is connected to 5 GHZ!!
When I switch the wifi settings to 2.4 GHZ the Mac mini works perfectly!!!
Googling this issue, a lot of people have reported Mac mini wifi problems and dropped connections...probably because of the aluminium case on the Mac mini and because the wifi card is at the bottom at the back and 2.4 GHZ has longer waves which are better suited to going through thick walls and other solid objects at longer distances?
I had a wifi extender and only put it only on the 2.4GHZ band and kept that in the same room as the Mac mini and only connected to the wifi extender which sped up the connection even more!
Hopefully this helps someone else!