Reluctant Raspberry

Note that this isn't about running LEDE on a Pi but the problems I'm having with RaspberryPi 3 as a client station over WiFi.
Firmware: LEDE Reboot 17.01.4 r3560-79f57e422d / LuCI lede-17.01
Router: Linksys WRT1900ACS
Out of 30+ other stations on my LAN, just this one is continually problematic. I am suspicious about the fact that when it does connect at boot, it shows up in the DHCPv6 Lease list as having an unlimited lease. I haven't altered the lease times (or anything else in the default config) since installing lede. All other stations show the default 12 Hour lease running including the small number of other devices using IPv6 so I don't get why the Pi is different.

The problem is that after a day or so it becomes unreachable from other clients on the LAN, as it seems to whenever I reboot the router (or cycle wifi down/up). I have it set up as a MQTT broker and consequently this breaks lots of things. I think I've checked all the obvious stuff (signal strength etc.) and it has been working without a hitch in this network for ages using the original Linksys firmware.

Unfortunately I'm not getting anywhere with this so I could do with some pointers.

Ideas: upgrade the router Wi-Fi driver to the latest from @eduperez (search forum for link) , make sure the pi itself has up-to-date drivers installed, and give this device static IP configuration both ipv4 and IPv6.

Cheers dlakelan, I'm very new to this project so have lots to learn. Not least the versioning! So what you're pointing out is that the 'master' release 17.01.4 contains relatively old WiFi drivers for the WRT ACs. OK, so I'll start there today.

I spent yesterday running an ethernet cable up to the loft where the Pi lives. I disabled WiFi on the Pi and got the IP that I had previously added to Static Leases. However, I'm having difficulty understanding how to get static IP configuration for both IPv4 and IPv6 as I am new to IPv6. I don't think my ISP provides me with a public IPv6 prefix anyway. Understanding the LEDE docs covering this area is proving to be difficult as I'm far from being a networking guru.

Public ipv6s these days all start with "2" as in 2xxx:xxxx:xxxx:xxxx:...:xxxx

the "Unique Local Addresses" that OpenWRT automatically sets up for you all start with fdxx...

Ok thanks. So I've got a unique local address then. Anyway, since using the etherenet cable everything seems fine with that Pi.

However, I also have a RaspberryPi Zero serving as an WiFi IP camera (also with static IP) and this too is only working for a day at most. Then I get ERR_CONNECTION_TIMED_OUT for http requests and I'm unable to SSH into it. However, while I also can't ping it from any computers on the LAN, I can ping it from the LEDE equipped router. It also continues to function and upload videos to a NAS also connected to the LAN. Rebooting the router then makes the Pi accessible again for a day.

I did wonder about the DHCP Lease timeout so set the lease time to one week but the "strange day" behaviour remains. How come it can communicate one-way (with the NAS) and return pings from the router but have no other routes?