It sounds like you’re trying to get your Spring Boot Admin server to properly handle the /actuator/threaddump endpoint for your services, but you're hitting a deserialization issue. The key problem is that Spring Boot Admin uses WebFlux and its WebClient to call your services, while your services are using standard Spring MVC (Servlet) stack. Since Spring Boot Admin's WebClient stack is reactive and has its own ObjectMapper configuration, it doesn't pick up your custom ObjectMapper settings, leading to the deserialization error when it tries to process the thread dump response.

Here’s how you can fix it:

Solution Overview: You need to ensure that Spring Boot Admin's WebClient uses the same ObjectMapper configuration that you've applied to your service, particularly the ACCEPT_SINGLE_VALUE_AS_ARRAY feature.

Steps to Fix It: Create a Custom WebClient Configuration for Spring Boot Admin Since Spring Boot Admin internally uses a reactive WebClient (through WebFlux), you can customize that WebClient so it uses your ObjectMapper with the correct deserialization feature.