I've intentionally looked for guys in my mafia on my rivals list to test this, and you can attack and rob them.

Please do not submit an ill-informed hacker ticket based on this.

Each henchmen that you have can only carry 9 items. One from each category I think. I have a question for you now. When did you send that ticket to support?
Each mafia member/henchman can carry 5 items, one each of gun, melee, explosive, armor and vehicle.
On Android the number of items reflects the number of unique items, so if you have 450 of one gun, and 50 of another then that would count as 2 in the "items used". It is unfortunate, but it is known and a ticket is unlikely to solve the issue.

The important thing to remember is that you are being given poor statistics, but that your attack and defense is not altered by this bug.
To demonstrate that fact, apply a simple logical test. If you are carrying 47 items into battle instead of the 500 you are meant to [figures are hypothetical], do you really think your true attack should be 10+X your shown attack?