Secured Linksys (Cisco) Access Point Connects Unsecured Randomly?

I live in apartment house that recently had a "professional" (I use that term loosely) sell and install a wireless network for Internet access. I am the only tenant with any knowledge of computers and networking, retired after 30+ years in telecommunications including 7 years in an ISP doing project management. I am also the only user who spends any appreciable amount of time online. The apt owner did not know of my background when he had this guy contracted to do the work. The "engineer" did an inadequate site survey, not thinking of or allowing for RFI, EMI, walls or other obstructions and he neglected to see what the tenants' individual needs were.

The installation was finished more than a week past his due date because "ran out of parts". When he did the individual user setups (he included that in his quote, apparently) he attempted to garner extra business by claiming that the end users' machines were all full of spyware, malware, viruses and worms. At least 3 tenants had brand new machines that had never been connected to the Internet and all three were purchased from different large vendors. I checked the others and out of 17 machines only one had any issues of that type.

There are 3 access points in the building, all with the same SSID to accommodate any tenants wishing to connect anywhere in the building or in the patio area, similar to a hospitality application. Problem:This "engineer" is now refusing to work on the network because he thinks it's a "difference of opinion" when to me, everything points to a possible defective access point or just lousy administration by this guy. The reason I've come to that conclusion is that at random, my secure connection (WPA2) drops and reconnects as unsecured.

The installer is convinced that random dropping, etc is because of my "defective machine" that never had any issues with dropping from a hardwired connection. He told the apt owner that a direct wired connection to the router would not work. Contractually, we tenants cannot contact him directly with service issues. My purpose is just to get decent access.