Tests on my end using a sample application built upon Spring Boot 3.1.2 and logback 1.4.11 work as expected.

Is it possible that you are running multiple instances of your web application inadvertently? Or is the output folder shared between multiple hosts?

More details are needed to investigate this issue. For example, can you provide details about the number of archived log files? Is it in the hundreds? What is the log production rate? How many megabytes of log output are produced per minute?