My current understanding of the grammar あげく is based on this common explanation I gathered online:
spending considerable time and effort doing an action, resulting in an outcome X + あげくY = “after doing much of X, Y finally/eventually resulted 「長時間～をした後、結局」
In these sentences, this explanation makes sense to me
いろいろ考えたあげく今年は日本に行くのをやめた。 After thinking and thinking about it, I decided not to go to Japan this year.
考えたあげく = spending a lot of time and effort thinking
何回も喧嘩したあげく、最後に離婚してしまいました。After a long series of arguments, we ended up divorcing.
喧嘩したあげく = spending a lot of time and effort arguing
However, the explanation above sounds weird and unnatural to me in these sentences:
なくしたあげく = spending a lot of time and effort lost?
忘れたあげく = spending a lot of time and effort forgetting?
I feel that there is another meaning of あげく I'm not aware of. Can someone explain how あげく is used in these instances?