It could also be a client-side problem where the strip software cannot maintain a server connection for long. This will require a firmware upgrade, which in turn requires a stable connection. What a mess…
Less likely though. If that was the case, switching off and back on the device would cause a reconnection, at least for a while. More likely to be server-side.
While the strip is switched to Wi-Fi, the connection is good (ping ~15-20ms), traffic seems normal for a few minutes and the strip can be controlled via Wi-Fi, e.g. a web browser. Then, it starts to flood the network with ARP broadcasts (who has <gateway address>? tell <strip address>), one every second or so, and, while it’s still connected and visible to the network, you cannot control it via Wi-Fi. It doesn’t matter if somebody responds to that ARP request or not, it keeps asking the same question.
As there is no option to “disconnect” from Wi-Fi, the only way to stop it is to power it off. I fear that if this can be fixed, it will require a firmware upgrade.
I deleted the LED strip from the eWeLink application and now I can’t add it again, the application detects but gives an error when trying to add it.
I recently had to change the DHCP server on my LAN, and suddenly the strips started working on Wi-Fi! So it’s definitely a software problem, not addressed by SONOFF. The previous DHCP server works for every other device I have (more than 50), except these L3-5M-P strips.
If that helps, the non-working DHCP was not on the router, and the strip kept asking ‘Who has < gateway IP >’. The working DHCP is on the router/gateway and the strip stops asking after the first broadcasted ARP ‘Who has < gateway IP >’ request.
I tested multiple times and the results are consistent. DHCP A does not work, DHCP B works. I’s been a few days now. I’m now able in January, to turn on my Christmas lights using Google Assistant when I’m not home 
Το έκανες να δουλεύει? Σκέφτομαι να δοκιμάσω αυτο με το παλιό router.
Με τον DHCP στο Synology NAS, έπαιρνε IP, αλλά μετά κόλλαγε το Wi-Fi. Ή φαινόταν εξ αρχής offline ή τό χανε μετά από 2-3 λεπτά. Με DHCP στο ZTE router φαίνεται σταθερό αρκετές μέρες τώρα.
Fixed
I found the 802.11b it work by
Wifi are connected by change HT 20 wide in 2.4G
Enable HT 20 in 2.4G
A years to fixed this problem
