@larrezz 

have you tested this firmware?

https://community.tp-link.com/en/business/forum/topic/710656

if it doesn't work, in some cases some problems can be solved if you do a factory reset of the device and readopt, you won't lose any settings so it doesn't hurt to try.

  @MR.S 

Thanks for the suggestions didn't know there was a beta version available. Will give it a try and let you know the results. 

 @MR.S 

I updated the firmware this morning and after the installation, all fixed ip addresses were pushed to the devices. After 2 hours the first tapo p115 device started to switch to a different IP. Should I maybe extend/disable the DHCP RENEW/RELEASE TIME? It's current set on 120 minutes. 

  @larrezz 

it's weird, I have about 25 P115 here myself but they don't have fixed ip, I set them to fixed ip on 3 units to test. I don't have an ER706W on this network, but an ER8411, I have another network with an ER706W, there are many devices that have a fixed IP via dhcp and there has never been a problem there either. dhcp lease of 120 minutes should be perfectly fine, but you can try to set it to 8 hours to see if it helps. I use 120 minutes leas time for the most on omada routers.