Espresso Machine issue:
As great as the Linea Classic is it really can’t handle high volumes. The GB5, Linea PB or Strada will preform much better from a water temperature stability aspect. Brew water is preheated through the steam boiler on the GB5, Linea PB and Strada where as the Classic is not. What happens with the classic is your bringing in too much cool/room temp water into the boiler and the heating element can’t keep up. Plus try your best to avoid using the hot water spigot on any espresso machine.
Grinder
You didn’t say what kind of Mazzer grinder you were using. In high volume cafes, I really don’t like to see anything but a Robur. Would still prefer a Mahlkonig Peak in high volume setting (but that is just more of a personal preference)