We recently returned from a week’s stay at the Lagunamar - Building 12, 4th floor. Each evening we enjoyed eating at a different restaurant in Cancun, returning to the resort between 8:30 - 9:00 pm. This particular building had its own lobby - no staff/ no lighting/no keyed entry at this time of night. Our room was next to the elevator. Having vacationed all over Mexico too many times to count, we have never encountered such a situation. Safety is always a major concern when traveling anywhere. We found the lack of security to be disconcerting.
The security team monitors access points, such as the main gate and beach entrances, to prevent unauthorized individuals from entering the resort premises. They do not specifically guard individual buildings, but I have observed them patrolling regularly.
IMO the corridors are well-lit and if I remember correctly there are security cameras on each floor of every building. In case you noticed any issues, such as a malfunctioning light near your unit you could have reported it.
I have never felt unsafe in any building within the resort, regardless of the time of day or night.
It is also important to note that the location is one of the safest in Mexico.