@Warri Is that TPlink switch controlled through Omada or is it an older one that omada can't control? 

I had a similar issue with some things disappearing. My issue came from having a omada switch connected to a  non omada managed switch was connected to a Omada Access point. 

Router >>> Omada managed switch >>>> non omada managed switch >>>>> Omada Access point and other connected devices 

The other devices on that non omada managed switch would get a dhcp address from the router then disappear from the list then the router would give those addresses to other things causing ip conflicts. But other devices on the other ports on my omada managed switch still was on the list, as well as anything going through the access points. It seems like if omada sees an omada managed device on the same port as regular clients it causes it to be confused. My fix was just replacing the down stream switch with an omada switch and everything was working normal.  

Not sure if this is any of help for you but just an observation I've seen. 

As for Solar Edge. I have solar edge as well and I noticed mine comes and goes throughout the day. The way I understand they only upload once every 5 minutes. And I'm assuming once it's done uploading it disconnects until it's ready to upload again.