I tried doing that several years ago, and it didn’t work.
So, I always click ‘Advanced’ then "Bulk Add Words’ - and have never had any problems. I normally use a spreadsheet, then copy-and-paste the items into the Bulk Add box, but I think you can probably just type in directly (remembering to tab-separate).
But I haven’t done this for a couple of weeks, so no guarantees.
I have just tried it out and it’s working ok for me.
If you are adding words individually (rather than by “Bulk Add Words”), when you try to add a word and have typed in the word (1) and the definition (2), what is the next step you take? If you click on the “+” to the left of the item, it should get added ok and allow you to add the next item:
Before adding any words, I always click on " + Add Level". This gives access to the “Databases” button, which opens up the various additional features (see the FAQs area).