I've been having this issue for a few months now and I'm not sure if it's android itself or SwiftKey. When I enter a text field, SwiftKey appears, I start typing then the keyboard goes away after a second or two then pops back up after a second. Normal functionality resumes the entire time until I need to type again.
It doesn't happen every time but it happens often enough that there isn't a clear pattern yet. It happens in all apps and all field types. I'm using a GS7 on the latest unrooted OS version.