In SwiftKey 3 we changed the way that fonts worked in efforts to reduce system resource usage. We know how valuable resources are to our users. As it turns out, a few people are experiencing some issues. We intend on resolving this issue as soon as we possibly can.
Please post the details, including the model of your phone, the version of Android you are running, and the languages you are using, on our feedback forum here so we can investigate the extent of the problem. We appreciate your patience and support in the meantime.