The net item has a special property which says:
When you use an action, bonus action, or reaction to attack with a net, you can make only one attack regardless of the number of attacks you can normally make.
Similarly, the Loading property says:
...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.
If I gain additional actions or reactions with which to attack with these weapons, can I make multiple attacks in one round?
For example, extra actions from sources like Action Surge:
...you can push yourself beyond your normal limits for a moment. On your turn, you can take one additional action.
...bonus action attacks from sources like War Priest:
...When you use the Attack action, you can make one weapon attack as a bonus action.
...reaction attacks from sources like Inspiring Surge:
...when you use your Action Surge feature, you can choose one creature within 60 feet of you that is allied with you. That creature can make one melee or ranged weapon attack with its reaction, provided that it can see or hear you.