What does this guard plate (arrow) tell me?

That your latch can almost certainly be slipped.

I don’t even need to go near the door to know what kit I need to bring.

Latch slipping has been a solved problem for a long time. Almost all commerical latches have a deadlatch plunger (circled) which should make it impossible to slip. If yours isn’t working, it’s almost certainly due to having the wrong strike plate installed or the gap between the door and the strike plate being too large (the case here – on a double door set up).

Neither of these cost a fortune to solve; likely far less than you spent on the lock. This lock costs around £200 before VAT; it’s currently providing the value of a £30 lock from Amazon (search for “low security digilock”).

To fix it requires kit and spares your estates team almost certainly has to hand, plus around an hour. Until you sort that, the intumescent strips on the door are creating a bigger obstacle to covert entry than your lock.