iPhone 5s apps crash while writing messages

Hello

My iPhone 5s apps 'Messages' and 'Messenger' for Facebook crash a lot, but only when I'm writing messages, not while reading them. The apps sometimes crash when I'm writing messages and they crash instantly when I hold my finger over the text, move the cursor around (the magnifying glass appears) and let go. They do not crash instantly when I move the cursor simply by tapping at another place in the text. Mostly the text message I am writing is not saved, but sometimes it is, or part of it is, when I reenter the apps. I am returned to the home screen, but the apps are still open when I double tap the home button.

I have the iOS 8.4.1 operating system - I recently upgraded, but I had the issue before the upgrade.

My Capacity is 26,7 GB and I have 9,2 GB available.

I have the latest version of the Facebook Messenger app.

I have tried turning it off and on again with no effect.

I have tried a hard reboot (pressing down the home button and the on/off/lock button at the same time until the device turns off and on again), also with no or limited effect - I think maybe the apps started, sometimes, saving the text message I am writing when they crash so it's not deleted when I reenter the apps - after the reboot.

Also, sometimes when I'm writing on my phone parts of my keyboard freeze, mostly it's the 'A' side (left side) of the keyboard. I don't think it's connected, but there it is.

Does anybody have the same problem and more importantly does anybody know how to fix it?