During the first phase of fermentation, your wild ferment is very actively bubbling, so it can quickly happen that the vessel overflows. This is not a bad thing at first, but a good sign of active lactic acid fermentation. That's why we recommend putting a plate underneath. Next time, make sure to leave more space to the edge of your vessel so that the vegetables can bubble in peace without overflowing.
What often happens when your ferment has overflowed in the first phase is this: In the second phase, when the bubbling stops and the juice in the jar sinks again, there is no longer enough brine in the jar to cover everything. Then you can top up your ferment with a 2% brine so that everything is well protected during storage.