EDITED BY MODERATOR: Moved to Bill of Materials space. Please post in the appropriate space when one exists. The API/Macros space is for if you are using the SOLIDWORKS API (Application Programmers Interface) or using/writing macros.
This is a known problem, new to SW 2019. It is fixed in SP3:
Drawings - Tables: Modifying column header (name) in the Bill of Materials (BOM) automatically adds slash ('/') before the header
When in BOM you insert a new column a pop up will come up that says Column Properties. You can select a dropdown that allows you to pick pre-made "Property Names" for most things you could need. Aside from that I was unable to find a way to get rid of the slash.
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