The striker (chrome thing) has an outboard notch AND a 3/8", fairly deep hole inboard of the notch. The door latch is a round beveled end "bolt" that is supposed to firmly drop into the striker hole when the door is latched. Likely problems are that the door is not closing far enough for the bolt to firmly drop into the striker hole. This causes the bolt to be caught only in the outer safety notch & not locked into the inboard hole. The door will never come open if the bolt is fully seated.
It's a little hard to tell when the bolt has dropped completely into it's striker hole, but if you're looking for it you will be able to tell.
If this is the case, the striker assembly can be adjusted outward to allow the bolt to drop well into the hole, maybe 1/4" of engagement. The striker mounting holes in the door pillar are slotted to allow adjustment. In a few cases, the holes must be elongated to allow the striker to move outward enough. The striker should be firmly mounted in it's support & just loose enough to rotate slightly, self align, when it meets the door slot. With proper adjustment, there should be a position where the door fits flush, the bolt fully latches, & requires only a little weatherstrip compression to latch.
Another possibility is that the latch/bolt assembly mounting is not adjusted far enough to the rear to allow the bolt to drop far enough into he striker hole. Or something in the latch/inner pull arm is not letting the bolt move far enough back to give positive engagement in the striker hole. Or maybe the whole works is binding. It would be very unusual for the striker to wear unless something is mis-aligned.
The striker can also be adjusted in the fore - aft direction by using shims between the striker & it's mounting plate. This gets a bit tricky due to the tapered, keystone, profile of the striker & it's receiving notch. The whole latch engagement can be changed by shimming the striker.
I'm sure that you can get it adjusted once you know what to look for.
D