@XtrimVR 

Hi,

The middle light is the "Powerline" indicator. 
When it turns off it means the connection between the two TL-PA717 (i.e. the connection through the buildings electrical wiring) has deteriorated to a point where no transfer of data is possible anymore. 

It could be that the quality of the Powerline connection was always marginal and has now become slightly more worse.
Do you remember if the data speed through the TL-PA717 KIT was always kind of slow?

It is also possible that the Powerline connection was originally good, but perhaps "a few weeks ago" some new electrical device (anything that plugs into a wall socket) has been added in your home that causes substantial interference in the electrical wiring.
 

  @woozle 

Hey, Thanks for replying.

I used to use WIFI and the interned speed was slow, about 5mbps. I then got the powerline adapters and it bumped it up to 30mbps. It was always a constant 30 and I don't think it was ever much slower than usual. About 1-2 weeks before the issues started happening I got a dehumidifier for my room. 
 

Could the dehumidifier be the cause of this or is it something else? 
 

I thought that maybe the powerline adapters may have overheating issues, since they get quite hot after a while (I do not recall if they used to do this before), but if they overheat I assume all the lights would turn off?

  @XtrimVR 

Well, the next time the middle light on the TL-PA717 turns off just unplug the power cord of the dehumidifier and see if the middle light turns on within a minute. If the middle light does not turn back on, then it's not the dehumidifier causing the problems.