I have a bunch of old BTC transactions between 4/10 and 4/12 that were confirmed long ago. But somehow today, they all suddenly appeared as not confirmed. Newer transactions are not affected.
Any ideas what's going on?
A confirmed transaction can drop to unconfirmed if was double spent when a block reorg had a different transaction. That doesn't happen a whole lot, and the transactions affected during the March 11th hard fork were the only ones since 2010 that a transaction with six confirmations on the longest chain reverted to being unconfirmed.
So if you had a confirmed transaction revert, it would have had just one confirmation most likely,
Check to see if the payments show on Blockchain.info.