It's quite common to not set a literal version directly in a dependency but use a property instead:
<!-- ... -->
<properties>
<mylib.version>6.0.1-20250909.132614-1</mylib.version>
</properties>
<!-- ... -->
<dependencies>
<dependency>
<groupId>someorg</groupId>
<artifactId>mylib</artifactId>
<version>${mylib.version}</version>
</dependency>
</dependencies>
unlock-snapshots (and I suppose lock-snapshots) doesn't seem to support such a setup because the respective property stays untouched after executing the goal, whereas the goal works as advertised with very same pom.xml when it's not using a property.