Sky Q and Booster Box

I’ve just upgraded to Sky Q (not a Sky broadband user) and was advised by the engineer that we needed a booster between the main box and the mini due to range issues (he said it was to be be on the safe side as it was borderline). All was fine for a couple of days but now the booster won’t connect to the Sky main box? This doesn’t seem to be an issue as the Mini seems to reach the main box fine - my understanding is that the boxes use a separate direct Wi-Fi mesh to the main BT one around the house, but multiple resets etc aren’t getting the booster connected.

Anyone else experienced this issue? It seems pointless to even use the booster if it’s not necessary?