Text Block Disappears, and Prior Correction is reversed

Hi. I am experiencing disappearing text blocks. I import text into my InDesign document via the Place command. When I try to edit the document, and insert the cursor, either all or a portion of the entire text block disappears. I Control Z to recover and make my correction, save, and move on. When I spot another correction I repeat the process and the text block again disappears, not every time, but sporadically. The worst part is that the correction I had made previously also disappears, even though I have been Saving after every single correction/addition. This began in late Deccember. I have uninstalled and reinstalled InDesign. I have swapped out mouses. Same issue.