I have to say I went trough hell and back. I started with around 80 online iot devices and by the time the number went down to about 50 showing up online and the offline register in the DECO App was counting up. I was facing several issues with the Ring camera system, my smart plugs at my marine tank as well as the Alexa control and Smart Life controlled lights. It was all messed up step by step. I was on a business trip for 2 weeks the Deco installed a new Firmware and also the new Mac OS Sequoia come out. Back home I updated all my Apple devices and I was in hell. I could not access IG or FB anymore either from mobile or computer devices, so I had to disable WiFi and go by 5G directly, my internet overall was very slow and I pointed it all out to the new Apple OS but I was wrong. Looking up in my smart life App 80 percent of my devices showed offline and regardless what I did it could not recover them back, device restart, Deco restart it all did not helped. I was very close to reset my whole network and start from scratch knowing it would maybe help but not solve my problem in a mid to long term perspective.

For those who don´t want to read the intro above here´s the solution:

If you look up in the Deco App you see your online devices, click on it and you see the list of devices online. Scroll down to the very end and you see the offline devices listed, expand the category of offline devices and DELETE them by swiping left or click on and then delete. 

DO NOT touch the online device category!

Don´t worry the Deco embed them back once they show up in the network automatically and they get back registered properly into the Deco system and your system works like a dream, smooth and fast and no malfunction anymore. IG and FB problems 100% solved.

As a conclusion to me by all the Deco FW upgrades, restarts and network reboots as well as device FW and OS upgrades some bad data is left behind that prevents the DECO from a proper relisting to online once they show up (A kind of I know you but not exactly symptom). Again I started with 80 iot devices around 15 other Hardware, I was down to 50 active devices and 78! offline devices, that showed my the number of bad or double entries was significant.

Often as troubleshooting you get told ignore your network and join back in, well that´s correct but DECO remembers you and if you don´t delete the bad entries in the Deco App under offline devices the bad entry is still there and will not resolve the issue until you have deleted them.

For me as a monthly routine, I will just delete all offline devices.

Note to TP-Link it might make sense to have a button the clean all offline devices or embed into the App this feature as a periodic routine you can run. 

My current setup:

1x BE65 5G (Center)

8x XE 75

Due to the fact of the setup of the house 2 floors + basement and garden facilities the amount of access points is necessary, also it´s a older builing with mixed materials and that fact eats out a lot of WiFi strength.