Why are records disappearing from MongoDB?

Question

MongoDB

There is a small project on Spring Boot, its essence is that it simply stores client requests in MongoDB. The project is not large and 2-3 applications come in a day.
The situation has already been repeated twice: 10-20 applications are hanging, you come in the next day - there is not a single one .... Where did they disappear to??? Only I have access to the admin panel.
It was 1 time, then a week later the same thing happened again.
What could it be? MongoDB stores data in RAM or what? And does not write to disk?
I understand if I had a million applications .... but here 10-20

Answer 1

It's hard to say without data from control and security tools, but in the light of recent events, this should not be dismissed: https://www.opennet.ru/opennews/art.shtml?num=45903
2 tips:
Monitor connections and other things.
Let system administrators close gaps in access to the database.

Answer 2

1) If you save to the database, then the record will remain there. (until it is deleted)
2) What prevents you from testing the script, how and where it saves.
Logics