Entries Changed to "Uncategorized"

Mast

Yesterday I discovered over 200 personal bank and credit card account
entries (each of them previously verified and then reconciled by myself)
mysteriously now appearing as "uncategorized". The vast majority
appearing between 2018 - 2022. Old printed reports show these same
transactions as categorized. These are frustrating & unwanted
changes. Can I remedy this? Is there a way to prevent this from
happening again?