I would like to suggest you try another software i.e.
CubexSoft OST to PST Converter. It is one of the best converter tools to convert multiple Outlook OST files to PST file format in Outlook 2019, 2016, 2013, 2010, and other below editions. It converts all emails, contacts, calendars, tasks, notes, and etc. from OST to PST format with attachments. It supports all the Windows OS like 10, 8.1, 8, 7, etc.