I have huntsmart app that had been working fine. Now I open it and it just goes away

If you already tried (to no avail) ALL the steps provided in the support article that led you here, I suggest that you contact that app developer/support team and ask them.

Use these instructions:--> How to contact an app developer - Apple Support

Regards

Giulio

Again, if you already tried (without success) the steps provided in the 4 sections of the support article, and if the issue is happening using that app only, neither we, just users like you, nor Apple can solve your problem, sorry.

Regards

Giulio