As for replay protection, when someone makes a contentious hard fork, they don't bother implementing it, because they want everyone follow only their chain. But when someone creates a forked altcoin, they do want to implement it, because it would make it easier for their users.
I know they should have implemented, but they didn't. BSV developers didn't want to implement it.
This is why you have to split your coins first. You can read about it here.
About replay protection:There is no replay protection between the BCH (ABC) and the BSV chains. This means that, unless you properly "split" your coins, transactions you make with one of those coins will also be made on the other.
Sending unsplit BCH will result in the same amount of BSV being sent to the same address (and vice-versa). The receiving wallet may not be prepared to accept BSV into their address, so there is a possibility of loss of BSV coins. This is not an issue specific to Coinomi, as any other wallet you use is under the same risk.
https://coinomi.freshdesk.com/support/solutions/articles/29000026274-bch-abc-bsv-fork-information-splitting