Warning Message shows twice before the record saves.

Summary

We want to show warning message once before the Lead record saves.

Content

Upon creation of the leads record, we have a validation rule that will check if the MMS ID is valid or not. If MMS ID is Valid, we want to show a warning message before saving the record. But we're encountering some issues, the warning message shows twice before the record saves. Is it possible to show the warning message once then when the user clicks the save and continue button again it will save the record instead of showing the message again?

For the script, please see the attached snippet. Thanks.