Make sure to schedule on the thread pool and not on the scheduler.

proxy/src/main/java/com/velocitypowered/proxy/scheduler/VelocityScheduler.java

@@ -185,13 +185,14 @@ public class VelocityScheduler implements Scheduler {
         @Override
         public void cancel() {
             if (future != null) {
-                future.cancel(true);
+                future.cancel(false);
                 onFinish();
             }
         }
 
         @Override
         public void run() {
+            taskService.execute(() -> {
                 try {
                     runnable.run();
                 } catch (Exception e) {
@@ -202,6 +203,7 @@ public class VelocityScheduler implements Scheduler {
                         Log.logger.error("Exception in task {} by plugin {}", runnable, plugin);
                     }
                 }
+            });
         }
 
         private void onFinish() {