Yikes! That sounds like a lot of security for a zoo!
A few things to check (sorry if some/most/all of these are already done. I'm just brainstorming here):
You mention that you've had 1 pick pocket caught and 1 vandal caught. But I think the same screen also shows the number of unique pick pocket incidents (or victims?), as well as maybe the number of vandalism incidences..... Remember that one pickpocket can steal from multiple people, and one guest on a vandalism rampage can destroy several things, each of which might count as a separate incident.
Next, I might check the security heat map to make sure that every square inch of guest-accessible path is covered by a blue sphere of a security camera -- with no gaps in between. (This will be harder to check since the guards also carry a roaming sphere with them. There's been lots of times where I've missed a section because the guards were there when I checked, but then moved out of range).
Next, I might try spending some time looking at the guest happiness heat maps, and the negative impact heat map. (maybe guest education too). And then I might check on animal happiness, and guest thoughts, and litter/bins/benches/atms, and the satisfaction level for your shops/food/drink places. Guests are more likely to vandalize if they're upset about something else, and given the level of security you've got, I'd imagine that there must be something (perhaps seemingly unrelated) that is causing them to act up despite knowing that they're going to get caught!
I've also noticed that if I've had protesters, or an escaped animal, I'll often see an increase in vandalism, either immediately during or soon after the incident. Sometimes by the protesters intentionally knocking things over, and sometimes by guests fleeing. (This is true even if the "escape" was a false escape, so if you've got any of the magic or bugged animals that can walk, swim, dive, or climb through walls, you may have trouble completing this challenge). Also, if you have crowded paths -- either normally or during a fleeing action -- items like benches, bins, atms can get damaged, so you might check if any of those path items can be moved off the path onto the curb/side (some can and some can't). Of course, then you still have to check to make sure the guests can still use/reach them.
One thing to note if you're coming to franchise after a long time playing in sandbox: Many of the things that that can be turned off or ignored in sandbox mode do have an impact on guest happiness (and thus vandalism) in franchise. I've seen guests complain about exhibit humidity, the number of plants in a habitat, terrain, the weather/temperature, levels of vendor training, the lack of gift shops or atms or bins or crowded paths. Lack of or misplaced education, or shop prices that are too high, or having to walk too far to reach something can all upset our fragile guests. In one of my earliest zoos, I had a guest go on a rampage and tear up bins, benches, and education boards -- and according to his guest thoughts, it was all because the number and gender ratio of my indian peafowl had gotten out of alignment! In another zoo, a guest responded to having an overflowing bin by knocking it over -- creating an even bigger mess, and making other people angry around him!
I realize it probably doesn't seem very helpful to say "check every other thing to see what might be up". But given how many security-specific items you've added, my instinct really would be that something else may be upsetting the guests and leading them to vandalize. So I really would just go through every single menu and heat map and animal/guest/staff/facility/habitat happiness panel I could find and look for anything that's in the yellow or red. (And if you're like me, I often have to take a moment to actively check myself whenever I'm tempted to think "that unrelated red alert about plants/terrain/pathing/atms/staff/enrichment/etc. can't possibly be the cause", and actively remember that it all is related through the guest happiness algorithms, and that at some algorithmic level the guests are picking up on that yellow/red alert and reacting to it in some way).
Good Luck!