While your waiting for an IK response, let me suggest that you may need to turn off dropbox syncing while your sorting this out. That's the only way I am aware of that can cause reminder reposting like your describing. The dropbox copy will have a complete copy of your MD database including reminders. If for some reason your PC database appears to be older than the copy on dropbox, MD will try to update your PC with whatever appears to be the most current. If you have some auto commit reminders, then duplicate entries can occur. I noticed a similar issue on my setup using Win 7-64 and MD 2017. I think this might be related to the time and date stamps saved on the dropbox copy. I noticed my main PC the clock was several minutes slow even with the time server turned on. My cell phone and other PC which sync through dropbox had accurate time. I think that discrepancy caused my reminders to be update oddly. Depending on how big a problem you have, I would tempted to restore a MD backup from a date prior to when your problem started. I think by default MD keeps backups going back 5 days.
On Windows, the backup files are stored at
You can confirm by clicking Help, Show Backup Folder
You will notice after clicking Restore from Backup the directory of the backup folder.
You should see your data set name expanded with the date.
Select the one you need and open.
That will restore everything back to that date.
Also remember to turn sync off until you can verify correct time on your PC.
I would certain recommend completing your tax returns before doing anything else.
I would suggest before starting to set up syncing that you delete all the existing Moneydance data out of drop box. Starting with a clean slate is always a good idea.
There have been some reported cases of syncing appearing to get confused and strange things happening, some instances have a very identifiable cause - we used to see it a lot when people stored their data file in their dropbox folder, in other instances it seems that something has thrown it out, as to what I have no idea, I suspect we have a lack of data on exactly what was happening on the computer in question.