Implement a new solution: Instead of static code blocks disabling logging, rollback slf4j-api, logback-classic, and logback-core to older versions. It's the addition of the rollback for slf4j-api that seems to restore logging.

src/main/java/ca/uhn/fhir/jpa/starter/Application.java

@@ -38,10 +38,6 @@ import org.springframework.web.servlet.DispatcherServlet;
 })
 public class Application extends SpringBootServletInitializer {
 
-	static {
-		System.setProperty("org.springframework.boot.logging.LoggingSystem", "none");
-	}
-
   public static void main(String[] args) {
 
     SpringApplication.run(Application.class, args);

src/test/java/ca/uhn/fhir/jpa/starter/CustomBeanTest.java

@@ -13,10 +13,6 @@ import org.springframework.boot.test.context.SpringBootTest;
 })
 public class CustomBeanTest {
 
-	static {
-		System.setProperty("org.springframework.boot.logging.LoggingSystem", "none");
-	}
-
 	@Autowired
 	some.custom.pkg1.CustomBean customBean1;
 

src/test/java/ca/uhn/fhir/jpa/starter/CustomInterceptorTest.java

@@ -23,10 +23,6 @@ import ca.uhn.fhir.rest.client.api.ServerValidationModeEnum;
 
 public class CustomInterceptorTest {
 
-	static {
-		System.setProperty("org.springframework.boot.logging.LoggingSystem", "none");
-	}
-
 	@LocalServerPort
 	private int port;
 

src/test/java/ca/uhn/fhir/jpa/starter/ElasticsearchLastNR4IT.java

@@ -57,10 +57,6 @@ import org.testcontainers.elasticsearch.ElasticsearchContainer;
   })
 @ContextConfiguration(initializers = ElasticsearchLastNR4IT.Initializer.class)
 public class ElasticsearchLastNR4IT {
-	static {
-		System.setProperty("org.springframework.boot.logging.LoggingSystem", "none");
-	}
-
 
 	private IGenericClient ourClient;
   private FhirContext ourCtx;

src/test/java/ca/uhn/fhir/jpa/starter/ExampleServerDstu2IT.java

@@ -23,10 +23,6 @@ import static org.junit.jupiter.api.Assertions.assertEquals;
   })
 public class ExampleServerDstu2IT {
 
-	static {
-		System.setProperty("org.springframework.boot.logging.LoggingSystem", "none");
-	}
-
 	private static final org.slf4j.Logger ourLog = org.slf4j.LoggerFactory.getLogger(ExampleServerDstu2IT.class);
 	private IGenericClient ourClient;
 	private FhirContext ourCtx;

src/test/java/ca/uhn/fhir/jpa/starter/ExampleServerDstu3IT.java

@@ -51,10 +51,6 @@ import static org.junit.jupiter.api.Assertions.assertTrue;
 
 public class ExampleServerDstu3IT implements IServerSupport {
 
-	static {
-		System.setProperty("org.springframework.boot.logging.LoggingSystem", "none");
-	}
-
   private static final org.slf4j.Logger ourLog = org.slf4j.LoggerFactory.getLogger(ExampleServerDstu2IT.class);
   private IGenericClient ourClient;
   private FhirContext ourCtx;

src/test/java/ca/uhn/fhir/jpa/starter/ExampleServerR4BIT.java

@@ -25,10 +25,6 @@ import static org.junit.jupiter.api.Assertions.assertEquals;
 	// when running in a spring boot environment
 	"spring.main.allow-bean-definition-overriding=true"})
 class ExampleServerR4BIT {
-
-	static {
-		System.setProperty("org.springframework.boot.logging.LoggingSystem", "none");
-	}
 	private static final org.slf4j.Logger ourLog = org.slf4j.LoggerFactory.getLogger(ExampleServerR4BIT.class);
 	private IGenericClient ourClient;
 	private FhirContext ourCtx;

src/test/java/ca/uhn/fhir/jpa/starter/ExampleServerR4IT.java

@@ -43,11 +43,6 @@ import static org.junit.jupiter.api.Assertions.assertNotNull;
 		// when running in a spring boot environment
 		"spring.main.allow-bean-definition-overriding=true" })
 class ExampleServerR4IT {
-
-	static {
-		System.setProperty("org.springframework.boot.logging.LoggingSystem", "none");
-	}
-
 	private static final org.slf4j.Logger ourLog = org.slf4j.LoggerFactory.getLogger(ExampleServerR4IT.class);
 	private IGenericClient ourClient;
 	private FhirContext ourCtx;

src/test/java/ca/uhn/fhir/jpa/starter/ExampleServerR5IT.java

@@ -41,11 +41,7 @@ import org.springframework.test.context.junit.jupiter.SpringExtension;
   })
 public class ExampleServerR5IT {
 
-	static {
-		System.setProperty("org.springframework.boot.logging.LoggingSystem", "none");
-	}
-
-	private static final org.slf4j.Logger ourLog = org.slf4j.LoggerFactory.getLogger(ExampleServerDstu2IT.class);
+  private static final org.slf4j.Logger ourLog = org.slf4j.LoggerFactory.getLogger(ExampleServerDstu2IT.class);
   private IGenericClient ourClient;
   private FhirContext ourCtx;
 

src/test/java/ca/uhn/fhir/jpa/starter/MultitenantServerR4IT.java

@@ -28,9 +28,6 @@ import static org.junit.jupiter.api.Assertions.assertEquals;
   })
 public class MultitenantServerR4IT {
 
-	static {
-		System.setProperty("org.springframework.boot.logging.LoggingSystem", "none");
-	}
 
   private static final org.slf4j.Logger ourLog = org.slf4j.LoggerFactory.getLogger(ExampleServerDstu2IT.class);
   private IGenericClient ourClient;