Bulked notification not sent every once in a while

I wrote a notification script that is capable of handling notification bulking. It works fine in single notification mode and I haven’t seen any problems with the first bulked notification. However, every second/third notification is not sent. It looks like the notification engine does’t call the script correctly and after a minute the following message is shown in notify.log:

2021-09-13 08:53:25,839 [20] [cmk.base.notify] Notification plugin did not finish within 60 seconds. Terminating.

As a test, I added a simple line at the top of the script, to find out if the script is called at all:

#!/usr/bin/env python3
# Bulk Pushover
# Bulk: yes

import os
import requests
import sys 

from cmk.notification_plugins import utils
import cmk.utils.password_store as cmk_pwstore

print (sys.argv)

bulk_mode = '--bulk' in sys.argv

When the notification script is called successfully, the arguments are printed in notify.log as expected. When the script is not executed successfully, they are not printed. That makes me think that the problem is perhaps not caused by the notification script itself.

I have raised the logging level for the notifications to “Full dump of all variables and command”, but that doesn’t give me anymore information on why the script is not executed.

Has anyone an idea why this is going wrong, or where I should look?

We’re using CheckMK CEE 2.0p9 by the way.

Does anyone know which process calls my notification script when there is a ripe bulk to be sent out and how I can check if it hangs ore anything?