Why does the compiler version go astray on every new dependency import via Maven or IDEA reload?

Question

Java

Hello!
Today I began to receive incomprehensible compilation errors with the above described algorithm of actions.
Who faced such a problem?

Answer 1

In pom.xml add properties

<properties>
        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
        <maven.compiler.source>1.8</maven.compiler.source>
        <maven.compiler.target>1.8</maven.compiler.target>
</properties>