docker app on heroku down, but won't start after sending request

Question

I have a spring boot rest api backend packed in a docker container and deployed to heroku under the free plan. It works and after a half hour it goes sleeping. But later, when I open the app and want to send some request, it doesn't start. I see from the logs, that the app was crashed.

Why is that? Why won't the app start? Why even was the app crashed, if it was shutting down gracefully?

Here is the log:

2022-02-27T19:58:05.770090+00:00 heroku[web.1]: Error R14 (Memory quota exceeded)
2022-02-27T19:58:22.938286+00:00 heroku[web.1]: Idling
2022-02-27T19:58:23.030649+00:00 heroku[web.1]: State changed from up to down
2022-02-27T19:58:23.707002+00:00 heroku[web.1]: Stopping all processes with SIGTERM
2022-02-27T19:58:24.136754+00:00 app[web.1]: 2022-02-27 19:58:24.136  INFO 3 --- [ionShutdownHook] j.LocalContainerEntityManagerFactoryBean : Closing JPA EntityManagerFactory for persistence unit 'default'
2022-02-27T19:58:24.158799+00:00 app[web.1]: 2022-02-27 19:58:24.154  INFO 3 --- [ionShutdownHook] com.zaxxer.hikari.HikariDataSource       : HikariPool-1 - Shutdown initiated...
2022-02-27T19:58:24.192171+00:00 app[web.1]: 2022-02-27 19:58:24.191  INFO 3 --- [ionShutdownHook] com.zaxxer.hikari.HikariDataSource       : HikariPool-1 - Shutdown completed.
2022-02-27T19:58:24.493677+00:00 heroku[web.1]: Process exited with status 143
2022-02-28T10:01:59.256200+00:00 heroku[router]: at=error code=H10 desc="App crashed" method=GET path="/" host=**** request_id=3e55141d-753c-4f91-b60b-2c78342f913a fwd="****" dyno= connect= service= status=503 bytes= protocol=https
2022-02-28T10:01:59.869943+00:00 heroku[router]: at=error code=H10 desc="App crashed" method=GET path="/favicon.ico" host=**** request_id=c64f6bb8-d9af-41ca-ac11-47cdc542eb32 fwd="****" dyno= connect= service= status=503 bytes= protocol=https
2022-02-28T10:02:29.304593+00:00 heroku[router]: at=error code=H10 desc="App crashed" method=GET path="/" host=**** request_id=9455eceb-fe52-41c4-9016-12496f2dce93 fwd="****" dyno= connect= service= status=503 bytes= protocol=https