This is a solution to phantom entries that doesn’t require scripts and is easily applied. Follow the instructions carefully.
There are two steps. The First Step is to create a backup of your course in MS Word. If you’re completely new to this, here are instructions. I made the instructions very detailed, but once you know how to do it, the procedure is straightforward and quick.
(1) In your browser, go to the course you want to fix and click on “Edit Course.” Once you’re in Editing Mode, make sure that what you’re editing is Levels, NOT Databases, Contributors, or Details. “Levels” should be highlighted blue. If it isn’t, just click on it.
(2) Now you’ll see all the levels as a stack of blue horizontal bars, each containing the title of the respective level. Expand each of these bars by clicking on “Show/Hide.” You’ll find that this will involve the least amount of scrolling if you do it from the bottom up. After you’re done, you’ll notice that the page as a whole has become very long. This is because each entry in the course is now displayed, and these could number in the thousands. Review the page to make absolutely sure that all levels are indeed expanded. Any level that is not properly expanded will not be included in the backup.
(3) Save the page by pressing Ctrl-S. In the “Save As” pop-up window that now opens, find a suitable folder, give the file your preferred title, and make sure to keep its .htm extension. There should now be two new items in the folder: the htm file and a subfolder containing its associated image files.
(4) Go to MS Word, while NOT quitting the Memrise page in the browser. From within Word, click on “Open”, locate the new htm file on your hard drive, and click on it. Once the file has loaded, save it, but with the extension changed to .doc or .docx. It is now a Word file, in which each level is visible as a table. By copying and pasting these tables (more on this later), you can recreate the whole Memrise course within 20 minutes or less. In other words, your data is now safe.
(5) Remove all columns and rows from the tables that do not contain the actual words to be memorized. I myself create courses with just one Latin word against one English word, so I need clean tables with two columns, nothing more.
(6) Ged rid of the “Alts” in each cell by doing a search and replace: Ctrl-H, then in the “Find What” line, type “Alts” followed by a space followed by the code for a paragraph mark. You can find this latter code by expanding “More” in the Search/Replace pop-up window, then expanding “Special,” and then clicking “Paragraph Mark.” The mark should show up as ^p in the “Find What” line. If the Alts + space has disappeared in that line, just retype them – before rather than after the paragraph mark. NEVER enter the paragraph mark by just typing ^p. That won’t work. The only way to get the proper code in the Search/Replace line is by the steps I just outlined. Don’t put anything in the “Replace With” line, and now click “Replace All.”
(7) If there is anything about the course that needs editing or correcting, now is the time to do it. Review and edit the tables in the Word File. Periodically save the file. Power outages can undo hours of work.
Having now completed the First Step, move on to the Second Step. This is to replace the existing database by one that is identical to it, but that doesn’t have the accumulated revision history which causes the phantom entries to appear.
(8) Go back to the browser where the course page should still be in Editing Mode. Leave “Levels” by clicking on “Databases.” In the dropdown menu that opens up, click on “+ Add New” and create a second database identical in structure to the first. This new database will be empty for now.
(9) Now comes the scary part: Click on the first Database in that same dropdown menu, and on the page that is displayed after the click, scroll to the bottom and locate the red button “Delete Database.” You’re now going to delete the first database, thereby emptying the course of all the entries it ever contained, including the phantom ones. You’ll be left with nothing but the second database, which is empty. Importantly, however, you will keep your accumulated score in the Leaderboard, and you will suffer no loss of points in your overall profile. But the course will treat all entries in the second database as ones you haven’t yet learned.
(10) While still in Editing Mode, leave “Databases” and go to “Levels”. Create at least two new levels, by clicking on “+ Add Level” and selecting the second database. In the blue bar of the first level enter the title of what used to be the title of the first level in the old database. (These level titles should still in the Word file.)
(11) Go back to the Word file, copy the table corresponding to the first level. You can do this by placing your cursor in any cell of that table, then clicking “Select Table” and then pressing Ctrl-C.
(12) Return to the browser. (It helps to have the browser and Word windows side by side on the screen.) Expand the newly-titled first level by clicking on Show/Hide. Now find the dropdown menu “Advanced,” which is top right under the horizontal blue title beam. Click on “+ Bulk Add Words.”
(13) In the pop-up window that follows, which is labelled “Bulk Add”, you’ll find the instruction “Paste Your Data Here.” Click anywhere in the box beneath it, and press Ctrl-V to paste the table that you’ve just copied. In that same pop-up window, find the blue “Add” button bottom-right, and click on it. Wait about ten seconds, and you’ll see the whole first level as if you had just spent two hours typing it in yourself.
(14) After this, do the same for all subsequent levels. Periodically click the green “Save and Continue” button at the very bottom of the page, just for safety – though you’ll find that Memrise is saving your new data anyway.
When you are completely done, you’ll have the whole course, revised to your liking, without any phanton entries whatsoever, but still showing the leaderboard scores of everyone who ever took the course. Other users may be upset that there is no record of the progress they had made in the course already – that information is gone. For all users, the course will now say something like: “0/1299 words learned”. That’s a bummer for sure. But at least they’ll be working with a course that reflects your intentions, without unwelcome bugs.
If you’re scared by the drastic nature of this method, find an old course that is no longer public, and see how it works. If you ever want to revise a course without creating new phantom entries in the process, you can implement that revision with the same method. But please do remember that this will reset to zero whatever progress users had already made, so I wouldn’t do it too often.
NB I do not know if this method can be made to work successfully in courses that involve media such as images or sound files. I’m only creating word-to-word Latin courses.