This is the 14052nd most frequent Russian word.
одномоментное
"Одномоментное" means "simultaneous" or "occurring at the same moment."
Here, "одномоментное" (simultaneous or at the same moment) describes the resolution of all issues occurring at once.
Одномоментное решение всех проблем далось нелегко.
The simultaneous resolution of all issues was not easy.
In this sentence, "одномоментное" (meaning sudden or occurring in a single instant) characterizes his appearance as happening unexpectedly and very quickly.
Его одномоментное появление удивило всех присутствующих.
His instantaneous appearance surprised everyone present.
Here, "одномоментное" (instantaneous or occurring in an single moment) is used in a negated context to emphasize that change takes time and cannot occur all at once.