Calendar entries gone

I'm using MS Office 2019 (however I have the same problem on MS Office 2010 so I don't think it's related to the office version). Recently I removed an email account (POP) and added it back (as IMAP), and then my calendar entries were gone. However, I don't understand how that could have caused the issue, as my calendar entries are saved in a separate file (Outlook.pst) which isn't related to the email account I removed and added back.
What's very strange: I can still see all the deleted items in the Outlook.pst file, however the actual calendar entries are gone (except 2 entries for some reason, those were there before; but I had hundreds).
I used the scanpst.exe on my Outlook.pst file, but no changes.
What may have happened here, and how to get my old calendar entries back?
Thank you Christy for having a look at my case.
It's the standard pst file which comes with outlook. It's not connected to any email account.
No import, it's the standard file.
I did it via Account setting. I did it in the same profile. However, as mentioned above, I don't think it's related to the removing and re-adding of the email account, because that email account has a separate pst (and no calendar entries at all). The issue is with the standard outlook.pst file which has the calendar entries saved.
Hi @Nick ,
Thanks for your reply!
Because I don't have your .pst file, the same test can't be operated. Considering the impact of the previously configured POP account, it is recommended that you try to remove the current IMAP account and configure the POP account again to check whether the previous calendar items exist. If it does exist, it is recommended that you try to export the calendar item(File>Open & Export > Import/Export > Choose Export to a file > Next > Click Outlook Data File (.pst)) and import the file after you are configured as an IMAP account.