With contract = new web3.eth.Contract(abi, addr),

The one and only reason for contract.methods.decimals().call() to throw:

Error: Returned values aren't valid, did it run Out of Gas?

Is if the contract deployed at addr does not implement function decimals().

With contract = new web3.eth.Contract(abi, addr),

The one and only reason for contract.methods.decimals().call() to throw:

Error: Returned values aren't valid, did it run Out of Gas?

Is if no contract which implements function decimals() is deployed at addr.