Nexus 5x with Android 7 beta 4. I've been using Swiftkey and it was getting pretty flaky. I would be trying to type my email address and I would look up and see it had suddenly skipped a space and added a couple of capital letters. I could see no pattern to what it was doing. I was having some other minor problems with various apps especially photos but that doesn't surprise me with a beta. Yesterday, I did a factory reset. All my apps, contacts, photos and so forth restored. I had to redo a few settings in specific apps. All I was actually missing were two ringtones I'd download. I checked the settings for Swiftkey and did uncheck the "auto inset prediction" feature.
In the interest of full disclosure, I did learn to type on an old Remington manual typewriter and that combined with short stubby fingers, and toes, I am a terrible typist on a virtual keyboard.
Yesterday evening I wrote some emails and did chores such as adding an email account and I was not longer having any problems with Swiftkey. I've been getting frequent updates for some of the apps. They're dealing with the beta, too.