The malfunction at the Signal chat service was resolved in the night from Saturday to Sunday.
Some users may see error messages and miss some messages due to Saturday's outage issues, the app's developer reports on Twitter.
The missed messages will reappear soon, Signal promises.
The problem was solved around 1.30 a.m. Dutch time.
"Signal is experiencing technical difficulties," the service wrote when the outage started Friday night.
"We are working hard to fix everything as quickly as possible."
The problems continued into the following night and morning.
At 2.00 a.m. Dutch time, Signal said "they are still working on getting extra capacity online as soon as possible".
The current servers would not be equipped in such a way that they can handle the crowds at peak times.
Signal is a messaging service similar to WhatsApp, Telegram and iMessage.
Signal's emphasis is on privacy: through the use of specialized encryption, messages cannot simply be intercepted by outsiders.
Signal is experiencing technical difficulties.
We are working hard to restore service as quickly as possible.
Author Signalapp Moment of Places 16:33 - 15 January 2021
Strong growth after changes to WhatsApp policy
The cause of the outage is unknown, but Signal recently saw its user base grow significantly.
This happened shortly after competitor WhatsApp introduced controversial privacy rules, allowing data from non-European users to be shared with Facebook.
Tesla CEO Elon Musk recently called on his Twitter followers to switch to Signal.