Forma Hardware issue or hidden process

[mzel]

I started noticing this issue some month ago on my Kobo Forma which is 4 years old. On the surface I see very slow response times to commands. For example opening the Kobo after wake up by the power button prompts for a swipe. If earlier it would take a bit more than a second to show the home page now it takes about 7 or 8 seconds. The same happens when switching to/from articles view.
OTOH when it is connected to wifi the upper right corner on the back starts to get warm, and then, obviously it drains the battery very quick.

I did try factory reset to no avail.
Any advice?