Compatibility issue between MemoQ and Trados 2015

Hello! We have a client who regularly sends us memoqxliff files and we have started having issues. When we import the files in Trados 2015, everything seems fine, but when we send back the target memoqxliff files, there is text missing. We can see all the text, they lose some text when they reimport the memoqxliffs created by us with Trados once the translation is finished. Does anyone know how to fix this? 

I tried putting memoqxliff at the top of the list in "file types" but haven't head from the client yet.

Thanks!