It's not only heat from LEDs but also from power unit that LEDs uses. They transform electricity from 220V sine wave (AC) here to 5V DC.
In 90% of cases where LED need replacement problem happens in this transformer unit. In rest 10% it's on LED fault - but it's also problem because they are series connected and when one is gone whole circuit stop. If they are parallel connected such issue won't happen.
The LEDs are not driven at 5V - that would be one of the worst voltages to be driven. The LED bulbs are driven approx at 3.2V x number of LEDs. (some LED chips may have 3-4LEDs in series as well)
In 90% of cases where LED need replacement problem happens in this transformer unit. In rest 10% it's on LED fault - but it's also problem because they are series connected and when one is gone whole circuit stop. If they are parallel connected such issue won't happen.