It seems like Logback is unable to recognize variable substitution for certain properties.

For example the scanPeriod property:

Logback configuration:

<configuration scan="${scan:-true}" scanPeriod="${scan-interval:-10 minutes}">
Specified to take default value of 10 minutes of logback property is not defined.

Logback properties:

scan=true
scan-interval=30 seconds
This property should override the default configuration of 10 minutes.

Logback error:
java.lang.IllegalArgumentException: String value [${scan-interval:-10 minutes}] is not in the expected format.

According to the Duration API, the duration format is correct.