If one zone goes into autohold mode, its timer stops advancing while the other zones timers do not. This causes the zones to get out of synch with each other. Some zones' may end up being one or more steps ahead of the others. In the past, we have tackled this problem by completely disabling the autohold. We discovered that this was NOT GOOD either.
Many customers rely on autohold without even realizing it.
When it disappeared it was noticed and missed. To resolve this quandary, the new zone variant stops the timers of all the zones whenever any zone goes into autohold mode. It is possible to include any number of channels in this zone scheme. If you could be sure that both 60 amp kilns would never be heating at the same time, you could still use all three. This is where the Digitry Power Sharing GB4 can help you out.