On the Dashboard you may notice that a contract is only appearing in monthly Expense and it's not below Total remaining obligation. It is because this contract is not related to an ongoing obligation but only to a monthly expense.
The contracts below Total remaining obligation are only the ones associated with money that you are obliged to pay and owe as a result of an ongoing contract obligation. An expense could be a one-time payment, an ongoing one until a contract is terminated or an obligation for a year or two, until it is paid off.
Not necessarily all expenses are obligations. For example a contract for a software subscription that is billed until the contract is terminated is a monthly expense but not an obligation. You will find it below Expense but not under Total remaining obligation. On the other hand obligations are money that your organisation owes as a result of signing a contract. This is an ongoing commitment. For example, if you sign a 24-month contract and pay monthly, this is an ongoing obligation and the contract will be below Total remaining obligation. But it is also a monthly expense so you will also see it as a monthly expense.