CompletableFuture: thenAccept called but whenComplete is not

Question

On an application where I run high traffic, I observe that sometimes post the completion of CompletableFuture the thenAccept is called but whenComplete is not. This issue is intermittent and tends to occur randomly and in a testing environment. I can reproduce it consistently in the end when I kill the running traffic and observe this behaviour. Has anyone seen such behaviour before?

This is where I initially register the exceptionally and whenComplete

rspCompFuture = rspCompFuture.exceptionally(ex->{
            logger.debug("Request: rspCompFuture is in exceptionally handling");
            ResponseEntity<byte[]> rsp = poolObj.getContext().exceptionallyCleanUp(ex, poolObj);
            return rsp;
        }).whenComplete((rsp, exe) -> {
            logger.debug("Request: rspCompFuture going in the when complete");
                        AppMetrics.getInstance().pegWhenCompleteCalled();
            poolObj.resetContext();
            PoolMgr.returnObject(poolObj);
            logger.debug("Completable Future Final Result onCompletion");
        });
        return rspCompFuture;
    }   

This is registered in between the code flow

rspCompFuture
                    .orTimeout(getTimeout(poolObj), TimeUnit.MILLISECONDS)
                    .thenAccept(rsp->{
                        poolObj.setAvailable(false);
                        AppMetrics.getInstance().pegThenAcceptCalled();
                        logger.debug("Transaction is completed");
                    });

So, once the future is completed this thenAccept is executed but it somehow just ignores the whenComplete call alltogether.