Hi Justin,
I apologize for the inconvenience caused.
This is an already known issue and we have a bug report regarding this.
DropDownBarItem hides when help text is shown in contained treeViewAdv control.
Regarding this issue you could track the status of this bug fix in the above link.We will try our very best to implement this at the earliest.
As a workaround you can refer the attached sample and let me know if this helps you.
Thanks for your patience and interest in Syncfusion products.
Best regards,
Deepa.T.S
DropDownBarItem_treeViewAdv.zip