diff --git a/locust_plugins/__init__.py b/locust_plugins/__init__.py
index 8c33754..47f5a43 100644
--- a/locust_plugins/__init__.py
+++ b/locust_plugins/__init__.py
@@ -1,4 +1,4 @@
-from .wait_time import constant_ips, constant_total_ips
+from .wait_time import constant_total_ips
 import locust
 from locust.user.task import DefaultTaskSet, TaskSet
 from locust import events
diff --git a/locust_plugins/distributor.py b/locust_plugins/distributor.py
index dae0f4a..de8e2c9 100644
--- a/locust_plugins/distributor.py
+++ b/locust_plugins/distributor.py
@@ -2,6 +2,7 @@
 import logging
 from gevent.event import AsyncResult
 import greenlet
+import gevent
 from locust.env import Environment
 from locust.runners import WorkerRunner
 
@@ -23,12 +24,8 @@ def __init__(self, environment: Environment, iterator: Optional[Iterator], name=
         if self.runner:
             # received on master
             def _distributor_request(environment: Environment, msg, **kwargs):
-                item = next(self.iterator)
-                self.runner.send_message(
-                    f"_{name}_response",
-                    {"item": item, "gid": msg.data["gid"]},
-                    client_id=msg.data["client_id"],
-                )
+                # do this in the background to avoid blocking locust's client_listener loop
+                gevent.spawn(self._master_next_and_send, msg.data["gid"], msg.data["client_id"])
 
             # received on worker
             def _distributor_response(environment: Environment, msg, **kwargs):
@@ -37,6 +34,14 @@ def _distributor_response(environment: Environment, msg, **kwargs):
             self.runner.register_message(f"_{name}_request", _distributor_request)
             self.runner.register_message(f"_{name}_response", _distributor_response)
 
+    def _master_next_and_send(self, gid, client_id):
+        item = next(self.iterator)
+        self.runner.send_message(
+            f"_{self.name}_response",
+            {"item": item, "gid": gid},
+            client_id=client_id,
+        )
+
     def __next__(self):
         """Get the next data dict from iterator
 
diff --git a/locust_plugins/mongoreader.py b/locust_plugins/mongoreader.py
index 87089fb..a2242d2 100644
--- a/locust_plugins/mongoreader.py
+++ b/locust_plugins/mongoreader.py
@@ -46,7 +46,7 @@ def __next__(self) -> dict:
         try:
             with dblock:
                 doc: dict = next(self.cursor)
-            self.coll.find_one_and_update(
+            self.coll.update_one(
                 {"_id": doc["_id"]},
                 {"$set": {self.timestamp_field: datetime.now(tz=timezone.utc)}},
             )
diff --git a/locust_plugins/wait_time.py b/locust_plugins/wait_time.py
index c7afb71..e7216a8 100644
--- a/locust_plugins/wait_time.py
+++ b/locust_plugins/wait_time.py
@@ -1,4 +1,3 @@
-import sys
 import logging
 import time
 from collections import deque, namedtuple
@@ -57,11 +56,5 @@ def func(user):
     return func
 
 
-def constant_ips(_ips):
-    """this function has been removed, now that it is available in locust.wait_time.constant_throughput"""
-    logging.error("constant_ips has been removed, now that it is available in locust.wait_time.constant_throughput")
-    sys.exit(1)
-
-
 def constant_total_pacing(seconds: float):
     return constant_total_ips(1.0 / seconds)