The placement of the word to be entered in the arabic sentence is not clear. Seems to be a problem of Duo not correctly switching between RTL and LTR.
It shows correctly for me. Might be your device not rendering and showing it properly?
Appears so in google chrome as well as in firefox (on windows 10 resp. windows 8.1)
I have the same problem and I use PC Firefox. It must be a common problem; I am using Mondly also for Arabic on Android and it has the same problem. So hopefully when one language program gets it working it might spread to others. I was like, but other language programs can do this. I haven't tried others, but apparently not. And my PC keyboard doesn't like to switch between Arabic and English in the same sentence in Firefox. So on both Android and Firefox I've seen the issue. It's only a matter of time before a fix is found and it spreads across programs.
This has nothing to do with the keyboard. Even when only reading the exercise, the empty space where you have to insert your text as well as the punctuation (period) is shown at the wrong place.