I'm not sure why this post went unnoticed for so long, sorry for the delay!
To add to Mike's reply, did you change any of the global configuration parameters? You can refer to this KB on where to check for changes: KB01630 - Manually Managing Global Configuration Parameters in Notifications 2.x
Was there any messages in the logs? Can you reproduce systematically on any Notification or is it particular to a specific Notification?
I am using PI Notifications Service 2017 (126.96.36.19965).
I did not have the attributes specified in the KB Seb provided.
In versions prior to 2.9.5, Two locations:
I have just created them now and will let you know what happens.
What version of notifications are you using? How are you formatting to two decimal places?