My IKEA lamps passing through a TRADFRI hub just disappeard all of a sudden. All the lights.xxx_name are gone and unavailable, but the switch.zzz_name are still visible - as is the hub. Here’s the kicker - all llights are visible in the IKEA app, alongside the switches.
I have tried to restart HA, restart the hub, inactivate the integration, re-install the integration, but the only thing I’ve acieved is to get the lights from unavailable to not being there at all. I have validated the lights by checking them into the hub once again with the IKEA dimmer, but to no use.
I haven’t messed with the lights at all for ages, but I did install a Raspbee 2 Zigbee controller the other day. And I restarted HA and had the lights present even after that was installed. To test, I deacivated the zigbee, but still no lights. As I am running out of ideas, please give me a gentle push in the right direction! 
Probably not what you want to hear, but I don’t use an Ikea hub for any of my Ikea Zigbee stuff, i pair it directly with a coordinator controlled by Home Assistant and use ZHA. never had an issue with a variety of smart plugs, lights and switches I have.
Yeah - not really. Had it since they launched without an issue. Strange that only the lights disappeared while the switches are present.
if anything, you should check the logs…
as we have been having trouble with the Tradfri Integration since beginning of this year, requiring it to be reloaded some 3-4 times away. Has nothing to do with the Gateway being faulty, or app, those all work robustly. As they have ever been.
It’s the integration that hasn’t been looked into seriously for fixing this unfortunately.
I am away from the home, but just checked in remotely, and can confirm all lights still being available, so it might be a setup specific issue.
have a look at the existing ones for a match in the logged errors, and ad to those. If not, open a new so the devs can investigate.
But, Logs are important so give them that and your diagnostic file found on the integration view.
I ended up taking a backup, then a roll back to my second to last backup and the lights were there again!
Then I restored my most recent backup, as I’d made some changes I really didn’t wanted to have to remake just to check - the lights were still there!
So problem solved! Still clewless about the cause though. 