Ok you need to back up your apps and settings. Go to settings, backup, apps and settings, then tap on backup now.
Once completed uninstall the app
Reinstall
Then the conversations you have had will be reapplied. The app is no good if you cannot open it. If you lose your conversations (which I doubt) it will be worth it to have the app functional on your phone.
I hope this helps. Nothing worse then a crashed or crashing app.
I have backup on for my phone's apps and settings, also in Whatsapp... I am afraid about losing recent conversations, because I don't know when the last backup was done, but I will do as you said, at the end at least I will have a working app... I hope
You can manually back up your phone in the backup section on settings. Like I said go to apps and settings and tap backup now. Once you have done this your backup will be 100% up to date. Don't uninstall the app until you have done the update
I did the uninstall/reinstall yesterday, and it fixed the issue. The only conversations lost were the ones that had unread messages, they were restored to the last backup. The other ones were alright.