It happened to me too. I guess there was an update of some sort, but the sOHM isn't actually "missing". Connect your metamask to Olympus, click on the button in the top right corner that has an "i" and the word OHM in it (i OHM). You'll see where it says Add Token to Wallet, select sOHM and add it. Click through the prompts. This will replace the sOHM custom token that's currently in your wallet. Refresh the page and you'll see your staked balance again. They must have changed the address or something but it's there…I was super nervous but I see my balance again now. All good.