Why does the streaming app constantly lock up?

Check your Internet connection strength. With a Internet speed test app. 

Speed test is fine. Internet connection is fine.

You missed the other posted question: "What streaming device or you using?"  or are you attempting to use the app running on the TV itself?

If you're using a native TV streaming app, then that's likely your issue. A stand-alone streaming device will perform much better. 

Originally was using a Firestick and the app was locking up. We then bought an actual smart tv and it’s still happening.

Right. SmarTV apps are never as good as stand-alone streaming devices. 

If I am not using my tv app what is another option?

I see you tried a firestick, and that would be a streaming device.  How old was the FireTV stick you used?

It was a brand new Firestick and within the last 18 months.

Could you be more specific than that as to the model?  For example, when they changed the base FireTV OS level that would support the U-verse TV application, someone complained that the FireTV stick they just bought 2 months ago wouldn't work.  Turned out he had just bought a FireTV edition that had been released over 3 years earlier.

So, I have no doubt that your FireTV stick is new, and you bought it fewer than 18 months ago, but that doesn't narrow it down much other than to say that it may not be one of the most recent generation of FireTV sticks released in September 2023 or later.

You can get a Gemini Dtv Stream box from Walmart for 40 dollars. Comes with a remote with channel numbers, guide button, dvr list button. It also has an ethernet port