The text of the Scout's Sudden Strike ability states:

Starting at 17th level, you can strike with deadly speed. If you take the Attack action on your turn, you can make one additional attack as a bonus action. This attack can benefit from your Sneak Attack even if you have already used it this turn, but you can’t use your Sneak Attack against the same target more than once in a turn.

The Loading keyword has the following text:

Because of the time required to load this weapon, you can fire only one piece of ammunition from it when you use an action, bonus action, or reaction to fire it, regardless of the number of attacks you can normally make.

So if a level 17 rogue was using a light crossbow, would they be able to make two attacks in one turn with the crossbow without taking the Crossbow Expert feat? I think yes, but I'd like to hear your opinions on the matter.

Yes. Once with action, once with bonus action. The loading property only stops multiple attacks with the same action.