Whenever qubic finds 2 blocks in quick succession, they don't publish them and instead keep building on them in secret as long as they are 2 block ahead of the public chain. When the rest of the network gets close to them and is 1 block away, they publish their longest chain and cause a reorg. Since they don't control 51% of the network if the rest of the miners/pools adopted a "first seen chain -1 n blocks" policy, so kept mining on the first seen chain as long as it's only 1 block shorter than the longest one the qubic strat wouldn't work and all their blocks would get re-orged instead.