During reconciliation, the starting balance is pulled from your last recon. The possibility exists that somehow this deposit had its date changed or some other action that corrupted your prior recon. Number one issue I get when I know something is there is that the date, by accident, was set to sometime after the statement date so it won't show until I unhide transactions after the statement date.
I would either delete your last recon and start fresh or run a new recon as of 12/31/19 with the correct ending balance, look at all transactions to be reconciled regardless of date. Sort the deposit list by amount to find the one that did not get checked off or got unchecked along the way. Verify the date on it or change it to be correct, finish (hopefully) that second recon for 12/31/19 and then your starting balance for January should be correct.
