@andrenb 

Firmware 1.5 is already released for M9 in EU and NA, but not everyone can get it through Deco app yet. You can visit TP-Link Support Web site, find firmware for your hardware version of M9, download it and install manually.

I've downloaded it, but I am going to hold a bit with upgrading my Deco M9 units: there have been reports of mesh units instability after upgrade, on that forum. My Deco mesh is stable and runs just fine, so I am on hold till it becomes clear if these were unrelated issues or brought by 1.5.

If you decide to upgrade manually and something is not right after upgrade, please share your experience on this forum.

@Alexandre. 
 

Ah, I didn't know that. I've only used that app as I thought it would be available there and I didn't see any posts on here about it. 
 

The 1.5.1-update has been working great on the M5's at our other house. I'll update manually next weekend when I'm at the house where the M9's are used. I have an extra set of three M9's in the box for another building which is not ready for another three-four months so if the 1.5 version is buggy I can set them up with the 1.4.3-version in the meantime until TP Link releases a bug fix. 
 

I'm using both the M5 and M9's in access point mode, that might be why the M5's haven't been making problems with 1.5.1 for me.

@Alexandre. Did the upgrade an regret it, satellite disconnect a lot and not possible to downgrade