Please note, from what I can gather, the prior suggestion of updating the Samsung keyboard will fix this issue in all instances. I have not heard otherwise. Please consider this the correct answer for this issue.
I'm having a similar problem on my Samsung J7 V. The Samsung Keyboard no longer works at all for me, and I recieve frequent pop ups saying "Samsung keyboard keeps stopping." These popups make it difficult to use the phone at all.
My solution to get the popups to stop, if not to get Samsung Keyboard working again, is to install two third party keyboard apps (Swiftkey, gboard, swype, google voice typing, etc). When you recieve popups, start typing into a text box using one of the third-party apps. Then, open the notification menu, tap on "select keyboard" and select the second third party keyboard app. The switch back to your main third-party keyboard.
In my case, this stops the popups. It doesn't make Samsung Keyboard work again, but it does allow me to use SwiftKey as my main keyboard app, and reduces the frequency of those annoying "Samsung keyboard keeps stopping" errors.
Hope this helps.