WiFi drops on Macbooks, where to dig?

Question

System administration

Dear community. Exhausted!
There is pfSense as a router, NetGear tp724 as a PoE switch, 5 Ubiquiti AP Pro points, about 40 Mac users (all Pro models, from 2010 to 2015, half for El Capitan and Yosemite), about 30 gadgets and 5-7 on Windows laptops. Only beeches from Apple suffer and fall off. Old Vaios work like clockwork, not to mention wired clients.
It manifests itself as follows - regardless of day and night, load or something else, at one moment one (many) of users raises an op, from his computer stupidly there is no ping even to the point to which he is supposedly connected. Sometimes it helps to simply turn off / on WiFi on the device, when this does not help, then overload the point through the controller.
There are 2 SSIDs, guest and combat, 2.4G on channels 11 and 6, 5G on channel 36. The air is quite loaded, played with power and channels. Didn't bring any result.
In Apple's TP, they say one thing "your network is not configured correctly." The maximum that has been achieved is that they recommend resetting the network settings on the device.
Declared, with the next update "WiFi issue fixed" personally do not spread to me.
I will be grateful for any advice.

Answer 1

We faced a similar problem, only mobile phones also fell off, and the constant reconnection of WiFi sucked the batteries to zero in a day. The problem was never fully resolved, since it was decided to rebuild the network completely with a different architecture and not waste energy on a temporary solution.
Perhaps you will be prompted to the right decision, if suddenly this is the case. Also on the FreeBSD router and Ubiquiti points.
In our case, the problem is the lease time of IP addresses from the DHCP server. Halfway through the lease period, the device tries to renew the lease, which most often fails for some reason... either the request does not reach the DHCP server, or the response from the DHCP server does not reach the user (by indirect evidence, it seems that it cut Ubiqiti). Different devices behave differently in this case - someone keeps their address until the last one and at the end of the lease period reobtains the address with a new one almost imperceptibly for the user, someone (mostly mobile) breaks the WiFi connection and reconnects, someone it simply releases the address without losing the signal.
Made life a little easier by increasing the rental time. But this, of course, is a big crutch.

Answer 2

Thank you.
The default DHCP lease is 7200 seconds.