In Google's Allo messenger, Swiftkey is unable to make a line break. All other keyboards tested (Swipe, Gboard, Samsung) have been able to make a line break across multiple phones, but every phone using with Swiftkey is unable to. This was also a problem several months ago but fixed itself in an update, but now unfixed itself a couple months back. The line break/enter key just does nothing, except will register as a backspace if the previous character is a space, and only a space.
Line breaks work fine in all other apps using Swiftkey.
Pixel 1 XL, all stock