I imported my June transactions from my main bank, did the review, and saw that the balances were off by about $700. Checked and saw that all May transactions had disappeared. Had to close up for the night, so returned to Quicken today and saw that more earlier chunks had disappeared, the green "new" dot had appeared next to all transactions all the way back and some entries from prior months that I had identified and categorized had returned to "check 2345" or "check 998866"
Then, when I fixed one of those prior transactions, it disappeared.