Writing a message with Swiftkey impossible, deleting the whole message while writing.

I've had this problem for quite long now in Android Swiftkey. When I try to write a message, at some point the keyboard deletes it completely. Not just last word, but everything, whole message. And obviously there is no undo or anything to have it back, so it's completely lost and very annoying bug.

I've not been able to recognize what the trigger for this is. It might be "space", or  ".", but "backspace" has done it also. It happens typically in mobile Firefox browser in a forum, but I've seen it happening also for example in reddit app, so I think it's not app related. Instead Swiftkey is having some bug.