Almost certainly data dependent. No markers on that line segment indicates there are no values in that range of X axis values.The line is apparently attempting to connect to some value that may be just past 01Jan08 but the XAXSIS range may be suppressing it from appearing.
Instructions here: https://communities.sas.com/t5/SAS-Communities-Library/How-to-create-a-data-step-version-of-your-data-AKA-generate/ta-p/258712 will show how to turn an existing SAS data set into data step code that can be pasted into a forum code box using the <> icon or attached as text to show exactly what you have and that we can test code against.
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