Text disappearing when opening Powerpoint file

Hello-- I am very new to Keynote and still trying to find my way around. had a very bad experience when a client sent me Powerpoint documents to be translated. It turned out that on some of the docs, text on several slides disappeared. The slides had images on them so I figured that they had no text until the client came back and told me that I hadn't translated the texts on those slides! I went back to the original files and the slides didn't have text on them. I quickly purchased Microsoft office, opened the files in Powerpoint and, sure enough, the text appeared! After trying to figure out what may have happened, I thought that maybe when I got the warning about the fonts (specifically Calibri) not being on Keynote, I should have clicked on "Change fonts" and wouldn't have had any issue. Alas, I found out that that didn't change anything after testing with a brand new file. The texts kept disappearing. Has anyone had the same or similar issues? This is really bad because I would never know when text is missing.