Zcoin with many orphan blocks - Some nodes need restart
The blockchain technology is fully decentralized including the hash calculation of the next block to be add in the chain. This characteristic increase the blockchain security, but also implies in many machines (aka miners) trying to hash the same block at the very same time and due this parallel processing it is possible of two or more miners to find an acceptable block hash and register it.
Two valid blocks in the same block height allow miners to use both blocks as source for mining the next block, creating parallel blockchains, but, as the information of a parallel blockchain is received, the miner will compare both and will mine in the chain that has more computational effort (main chain -- blue blocks above). Since all miner will do the same thing, with some time all miners will converge to the main chain stopping the mining process from orphan blocks (green blocks).
To maintain a masternode online it is necessary to be synced to the main blockchain, hence all the nodes and wallets that were in sync with the green chain, need to rewind and sync to the main chain. This rewind process may take long enough to happen or do not happen properly and requires a blockchain fix to allow the node to sync back again, in both cases the masternode will require a new start. There are many other things that take part in this process as the project coding, protections, ban limits due node behavior and etc. Also, if the wallet was offline during the split process it will only download the data from the main chain.
There is a consensus that this task of checking the node and restarting it is a portion of the duty attached to the masternode reward, and since orphan blocks are random, as are the chance of the node staying in it, in the long game, all masternodes shall earn the same reward.