The bypass capacitor value depends on how much the current required by the load, the WiFi module in this case.

What I think happened in this case is that the charge in supply capacitor inside the module gets depleted faster than charge being supplied by the bypass capacitor thus deactivate the WiFi. I suggested that you use a slightly higher value.

I wonder if they tell you what is the capacitor value to be used since it is not supplied with the product.

People have to be smarter to create such device. It is programmed by human also. So, the smart device is not really accurate to describe those devices

Seller is smarter than switch and you

It could not be more than the one with N wire.

Not much difference anyway. Some items go cheaper after 10/10. Some stay same prices.

Problem during sales is couriers sent wrong planets, lost, wrong orders

Yes, intermittent like that is very likely due to faulty board because logic voltage leakage in circuitry.

Crowd funding?
Put everything in a basket?

If your house is single phase no problem but if 3-phase might not work.

Not necessarily. If the L and the N from same phase , should be working ok. If N from other phase might not work but depends on how the wiring I believe. If each phase is on RCD type breaker, then it may not work because imbalance between L and N (current go out from L and return through N not balance because measuring different circuit). Can try first.

I think to have or not to have N depends on if the power generated is enough for that module to operate without N. If not, the design require N.

What is the switch rating and what is load like?

Looks like that switch cannot handle kickback voltage when switching off or the current surge during power on from the fan. The lamp is simple resistive load unlike inductive load (motor).

During power off, inductive load such as motor winding will create voltage spike during power off. This probably damaged the electronic components in the switch. The fan probably did not have good snubber circuit to suppress the spike and so does the switch.

What a fuss having or not having capacitor? I thought in Malaysia most house has no N at switch.

Most contractor after cut through cement plaster will do bad job plastering it back. Those house with trunking maybe lucky if can just pull additional wire.

If you don't mind having wire trunk on surface, then no problem. N wires are looped on ceiling instead of at switch to save cost since it is not a requirement in Malaysia unlike certain countries.

The zigbee 20A switch is same brand with others?

I don't thing it has anything to do with wiring. Perhaps the orientation of the switch due to its location. This affect signal polarity thus affect reception of signal.

The 20A switch to air-cond or water heater by rule is only single point direct to 20A MCB. So, the limit is the MCB rating there. How many light switch can tapped? No simple answer.

The N wire is the return current flow path from load. If there is 10A current flow through L to the load, then the same 20A current return to the MCB through N wire. If your 20A switch already is carrying max 20A already, then any more load added will trip the MCB. You do not need to on the switch if you tap the N side that enter the switch, not the N after the switch.

There are conditions:
If the 20A circuit is going through RCCB, then tapping the N wire the the 20A circuit will trip the RCCB.
If your house is 3 phase wiring and the N you are tapping is from another phase, it may not work.

I think depends on type of dimmer. The more common one use triac. Just require series connection like you mentioned. It can be leading or trailing edge dimmer. Work with some LED but mostly don't. The trailing type a bit more expensive and more compatible with LED. They only work for resistive load only. The PWM dimmer need separate power to operate. This may require N usually.