This can be strange but there must be some explanations.
This BH owner happened to install a CCTV camera inside his BH.
He installed them because he wanted to know why on many occasions the eggs went missing.
It was a big mystery and he was hoping that he can find out the answer.
There were a couple of things he observed by this strange act by a bird removing eggs from a nest seems to attract his attention.
He posted in a WA group and ask for explanations.
"Why did the swiftlet removed her own egg?"
What came to my mind are the following possible reasons:
1) Those 2 eggs have expired or could not hatch even after the incubation period. The couple sensed that their eggs have problem to hatch so they might have removed their egg so that they can start laying a new set of eggs.
2) My next theory is that this nest was taken over by a more dominant couple who wanted this corner of the BH very much. They took over and quickly remove the old set of eggs. You can see that just after the egg removal she begin to repair the seat inside the nest.
3) My next theory have to do with the accidental touching by the BH owner. He must have touched them with his bare hand and his sweat must have come in contact with those eggs. Once the bird returned home and smell something odd she will remove those eggs.
4) My next theory have to do with the eggs was not hers in the first place. There are people who will replace the real eggs with other eggs taken from another nest. There are people who have asked me to buy large size swiftlet eggs. They wanted to populate their BH with a new and bigger species. Once the mother realized that those eggs were not hers she will quickly remove them.
5) This next theory might be a bit odd but it is not a laughing matter. The male is a sex maniac. What he did was to remove his own egg in order to get his spouse to be on the heat again. Usually female swiftlet will get "on the heat" when they have nothing to do. Example once their babies took off within 10 days they will lay the next clutch of eggs. Which mean two days after those babies left the female will be on the heat again.
6) One of the group member think that it might be due to the high temperature. The owner have yet to reply on this issue while I am writing this article.
You might have you own explanation but it is interesting to learn more about their behaviors.