HTTP 415 Unsupported Media Type Warning - Source unkown

I am woring with the latest nightly and have on regula bsis the following warning in the logs

2021-02-22 22:25:35.907 [WARN ] [s.impl.WebApplicationExceptionMapper] - javax.ws.rs.ClientErrorException: HTTP 415 Unsupported Media Type

	at org.apache.cxf.jaxrs.utils.SpecExceptions.toHttpException(SpecExceptions.java:117)

	at org.apache.cxf.jaxrs.utils.ExceptionUtils.toHttpException(ExceptionUtils.java:168)

	at org.apache.cxf.jaxrs.utils.JAXRSUtils.findTargetMethod(JAXRSUtils.java:514)

	at org.apache.cxf.jaxrs.interceptor.JAXRSInInterceptor.processRequest(JAXRSInInterceptor.java:181)

	at org.apache.cxf.jaxrs.interceptor.JAXRSInInterceptor.handleMessage(JAXRSInInterceptor.java:78)

	at org.apache.cxf.phase.PhaseInterceptorChain.doIntercept(PhaseInterceptorChain.java:308)

	at org.apache.cxf.transport.ChainInitiationObserver.onMessage(ChainInitiationObserver.java:121)

	at org.apache.cxf.transport.http.AbstractHTTPDestination.invoke(AbstractHTTPDestination.java:267)

	at org.apache.cxf.transport.servlet.ServletController.invokeDestination(ServletController.java:234)

	at org.apache.cxf.transport.servlet.ServletController.invoke(ServletController.java:208)

	at org.apache.cxf.transport.servlet.ServletController.invoke(ServletController.java:160)

	at org.apache.cxf.transport.servlet.CXFNonSpringServlet.invoke(CXFNonSpringServlet.java:216)

	at org.apache.cxf.transport.servlet.AbstractHTTPServlet.handleRequest(AbstractHTTPServlet.java:301)

	at org.apache.cxf.transport.servlet.AbstractHTTPServlet.doPost(AbstractHTTPServlet.java:220)

	at javax.servlet.http.HttpServlet.service(HttpServlet.java:707)

	at org.apache.cxf.transport.servlet.AbstractHTTPServlet.service(AbstractHTTPServlet.java:276)

	at org.eclipse.jetty.servlet.ServletHolder.handle(ServletHolder.java:852)

	at org.eclipse.jetty.servlet.ServletHandler.doHandle(ServletHandler.java:544)

	at org.ops4j.pax.web.service.jetty.internal.HttpServiceServletHandler.doHandle(HttpServiceServletHandler.java:71)

	at org.eclipse.jetty.server.handler.ScopedHandler.handle(ScopedHandler.java:143)

	at org.eclipse.jetty.security.SecurityHandler.handle(SecurityHandler.java:536)

	at org.eclipse.jetty.server.handler.HandlerWrapper.handle(HandlerWrapper.java:127)

	at org.eclipse.jetty.server.handler.ScopedHandler.nextHandle(ScopedHandler.java:235)

	at org.eclipse.jetty.server.session.SessionHandler.doHandle(SessionHandler.java:1581)

	at org.eclipse.jetty.server.handler.ScopedHandler.nextHandle(ScopedHandler.java:233)

	at org.eclipse.jetty.server.handler.ContextHandler.doHandle(ContextHandler.java:1307)

	at org.ops4j.pax.web.service.jetty.internal.HttpServiceContext.doHandle(HttpServiceContext.java:293)

	at org.eclipse.jetty.server.handler.ScopedHandler.nextScope(ScopedHandler.java:188)

	at org.eclipse.jetty.servlet.ServletHandler.doScope(ServletHandler.java:482)

	at org.eclipse.jetty.server.session.SessionHandler.doScope(SessionHandler.java:1549)

	at org.eclipse.jetty.server.handler.ScopedHandler.nextScope(ScopedHandler.java:186)

	at org.eclipse.jetty.server.handler.ContextHandler.doScope(ContextHandler.java:1204)

	at org.eclipse.jetty.server.handler.ScopedHandler.handle(ScopedHandler.java:141)

	at org.ops4j.pax.web.service.jetty.internal.JettyServerHandlerCollection.handle(JettyServerHandlerCollection.java:80)

	at org.eclipse.jetty.server.handler.HandlerWrapper.handle(HandlerWrapper.java:127)

	at org.eclipse.jetty.server.Server.handle(Server.java:494)

	at org.eclipse.jetty.server.HttpChannel.handle(HttpChannel.java:374)

	at org.eclipse.jetty.server.HttpConnection.onFillable(HttpConnection.java:268)

	at org.eclipse.jetty.io.AbstractConnection$ReadCallback.succeeded(AbstractConnection.java:311)

	at org.eclipse.jetty.io.FillInterest.fillable(FillInterest.java:103)

	at org.eclipse.jetty.io.ChannelEndPoint$2.run(ChannelEndPoint.java:117)

	at org.eclipse.jetty.util.thread.strategy.EatWhatYouKill.runTask(EatWhatYouKill.java:336)

	at org.eclipse.jetty.util.thread.strategy.EatWhatYouKill.doProduce(EatWhatYouKill.java:313)

	at org.eclipse.jetty.util.thread.strategy.EatWhatYouKill.tryProduce(EatWhatYouKill.java:171)

	at org.eclipse.jetty.util.thread.strategy.EatWhatYouKill.run(EatWhatYouKill.java:129)

	at org.eclipse.jetty.util.thread.ReservedThreadExecutor$ReservedThread.run(ReservedThreadExecutor.java:367)

	at org.eclipse.jetty.util.thread.QueuedThreadPool.runJob(QueuedThreadPool.java:782)

	at org.eclipse.jetty.util.thread.QueuedThreadPool$Runner.run(QueuedThreadPool.java:918)

	at java.base/java.lang.Thread.run(Thread.java:834)

From the message itself i could not find the source, so i startet to disable things step by step. Currently no things are enabled, but the message still pops up every 3 minutes.

Has anyone an idea or a hint work get rid of this warning.

Thanks
Thomas

Similar issue, slightly different circumstances