Use Maven-build-cache for submodules under parent pom

I have a maven project with 2 modules and a parent pom as such

<modules>
    <module>api</module>
    <module>service</module>
</modules>

I would like to take advantage of the maven cache extension and I've added it in the build section of the parent pom as such

    <extensions>
        <extension>
            <groupId>org.apache.maven.extensions</groupId>
            <artifactId>maven-build-cache-extension</artifactId>
            <version>1.0.0</version>
        </extension>
    </extensions>

I've also added a maven-build-cache-config.xml file however it would seem that every time I run mvn clean package a different checksum is generated for my submodules and as a result I don't actually benefit from the caching since all my java files are in those submodules

I've tried multiple configs with no luck unfortunately

<?xml version="1.0" encoding="UTF-8" ?>
<cache xmlns="http://maven.apache.org/BUILD-CACHE-CONFIG/1.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
       xsi:schemaLocation="http://maven.apache.org/BUILD-CACHE-CONFIG/1.0.0 http://maven.apache.org/xsd/cache-config-1.0.0.xsd">
    <configuration>
        <enabled>true</enabled>
        <hashAlgorithm>XX</hashAlgorithm>
    </configuration>
    <input>
        <global>
            <glob>{*.java,*.xml,*.properties}</glob>
            <includes>
                <include>recursive=api/*</include>
                <include>recursive=service/*</include>
            </includes>
        </global>
    </input>
</cache>

How can I make this extension actually cache the contents of my submodules with the same checksum if there haven't been changes. I know this extension is fairly recent and I haven't been able to find any hits online.

EDIT

Commenting one of the child modules out, actually ended up working and the cache is kicking in correctly. Is it possible there's a limitation to the extension in that it scans for a single module?

Solution

It turns out the issue was a "false alarm". In my api module I have a swagger file which would generate POJOs in the ignore-generated folder, so the fix is to add the following within this particular module and then everything is working as expected with proper caching in place.

<properties>
        <maven.build.cache.exclude.ignore-generated>${project.basedir}/ignore-generated</maven.build.cache.exclude.ignore-generated>
</properties>