Where PST contacts break during cross-platform transfer?

[Brinshalom01]

I recently tried to move my contacts from a PST file created in Outlook on a Windows system to a different platform (such as a web-based email service or a mobile device). The import process completed without any major errors, but many contacts were missing important fields like phone numbers, job titles, and custom notes. Some contacts were also duplicated, while a few did not appear at all after the transfer. My main concern is understanding where PST contacts usually break during cross-platform transfer.