When an entity with an Instant field is persisted and then retrieved, the instants before saving and after retrieving are different when the original Instant was a DST end.

It was probably introduced by this commit which is associated to this ticket.

Here's a demo repository.
When executed, it will produce the following logs which shows the difference between the instants:

com.example.demo.DemoCommandLineRunner   : System timezone: Europe/Paris
com.example.demo.DemoCommandLineRunner   : Instant before save: 2018-10-28T01:00:00Z
com.example.demo.DemoCommandLineRunner   : Instant after find: 2018-10-28T00:00:00Z

It happens since version 5.4.2.
Uncomment line 19 in the pom.xml of the demo in order to test with version 5.4.1 which will produce the following logs:

com.example.demo.DemoCommandLineRunner   : System timezone: Europe/Paris
com.example.demo.DemoCommandLineRunner   : Instant before save: 2018-10-28T01:00:00Z
com.example.demo.DemoCommandLineRunner   : Instant after find: 2018-10-28T01:00:00Z