You could always try unplugging and removing the batteries (V2) from your hub for @15 minutes. When you plug it back it, it will rebuild the network.
I had problems with my Kwikset dropping off, so I bought this: https://www.amazon.com/gp/product/B07MVX4M2Q/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1
And put it in the room right next to the front door lock. I’ve had zero problems with it since then.
[EDIT] I was suspicious and checked your post again
I’m not sure about the new app, but I thought this functionality was removed from the old app. I had to create a piston in Webcore to lock/unlock the door. I’ll check again.
[EDIT] My bad. The ST classic app works. I guess it’s Alexa that won’t let you unlock the door.