@PedroKTFC 

Hello, I'd like to collect some info to locate the issue:

1. How did notice that it is overheating? Is it displaying on the Kass app? Can I have a screenshot? 
2. May I know where the HS100 was used, like in the kitchen, bedroom, living room, etc.?
3. The HS100 was plugged into a wall socket or a power strip? Near the location where the HS100 was working, are there any other High-power appliances, such as the heater or air conditioning?
4. Which devices did you plug into this HS100 and how about the power load it requires when it's functioning? If you do not plug anything into HS100, will it become hot?
5. If you plug HS100 into a different location, will it work fine?
6. How about the room temperature? And how frequently this overheating message popping up?

Here are some tips:
1. Put your HS100 in a dry and open environment, avoid placing it in a closed space, don't let it suffocate.
2. Avoid placing your HS100 on top of any running electronic devices.
3. Keep your HS100 away from direct heat (like fireplaces and space heaters) or excessive sunlight.

Thanks.

@Brook 

1. How did notice that it is overheating? Is it displaying on the Kass app? Can I have a screenshot? 

I first noticed when my monitor went off! I then saw it on the Kasa app and it stayed off with the overheat set. Unfortunately I've disabled it for now as it's screwing up my integration with google home so I can't give you a screenshot.
2. May I know where the HS100 was used, like in the kitchen, bedroom, living room, etc.?

It was in my study.
3. The HS100 was plugged into a wall socket or a power strip? Near the location where the HS100 was working, are there any other High-power appliances, such as the heater or air conditioning?

It was plugged into a wall socketwith nothing else nearby.
4. Which devices did you plug into this HS100 and how about the power load it requires when it's functioning? If you do not plug anything into HS100, will it become hot?

There was a desk lamp and monitor. When I tried it by itself it did not get hot.
5. If you plug HS100 into a different location, will it work fine?

Nope, tried that.
6. How about the room temperature? And how frequently this overheating message popping up?

I'm in England, room temperature was warm but not excessive! The overheating message in the Kasa app remained throughout until I removed the device from the app.

Here are some tips:
1. Put your HS100 in a dry and open environment, avoid placing it in a closed space, don't let it suffocate.

Was in an open wall socket.
2. Avoid placing your HS100 on top of any running electronic devices.

Ditto above.
3. Keep your HS100 away from direct heat (like fireplaces and space heaters) or excessive sunlight.

There were none around.

@PedroKTFC 

Hello, thanks for your detailed reply.

Do you mean there is a lamp and a monitor plugged into this HS100? May I know the model number of the lamp and monitor? Do you know how much load do they need when functioning properly?

As per your description, the plug will not be hot when there is no device plugged in, will it show 'Overheat detected' if there is no device plugged in?

How many Kasa plugs do you have in total? Are others working just fine? May I have the MAC address of this problematic one?

Thanks.