The AfterLoading event is used to pre-fill data in transient fields defined in custom objects or extension objects. We have seen cases where developers have raised error/warning/information messages in the ABSL scripts for AfterLoading event.
However, we have certain framework limitations which do not allow raising error messages in a lot of cases in the AfterLoading event. We therefore have decided to stop this function and recommend you to change the code and move the raising of the messages to other event scripts.
From the November 2018 release, if you try to raise messages in the ABSL script, you will get a warning that raising messages is not allowed. The framework will ignore the raising of messages in the AfterLoading event to prevent runtime dumps due to the above explained issue.
And with the February 2019 release, you will not be allowed to raise message in ABSL for AfterLoading event. You therefore are required to change the logic for consistency and raise the message in other ABSL scripts, such as, validations etc.