arc - Reason for short current burned the PCB board between 24A 220V relay for 2000W Univetsal Vacuum Cleaner motor

We have one power source board with 24A 220V like this:

One of the relay control 500W heater and second one control the 2000W vacuum cleaner motor like this:

The problem is we have one arc between two pins of the 2000W motor which burned the PCB like this:

And

Which the short current happened here:

So the tracks are based on the location of relay pins and the distance between them cannot become more.

The question is here:

How and Why this arc happened? Does it because of the thickness of the copper on The PCB Board if yes, as you can see the PCB Tracks line which have height current were soldered, So how this happened with this condition?Could this because of startup current usage of the universal vacuum cleaner characteristics?

UPDATE:

The location of the PCB Board inside the device vs Motor is shown here:

Thanks for your attention.