This is a Samsung issue, but it is not related to the new app, it is related to the new SmartThings Alexa skill. 
Smartthings is aware of it and is working on it. There is nothing you as a customer can do to fix it so don’t waste time on that.
Right now it is very erratic. It may work for a while, then work with a delay, then stop working… Sometimes the device status updates in the Alexa app, but the routine doesn’t trigger. Sometimes the status doesn’t update either. It will absolutely drive you bananas. But, again, all we can do is wait for it to get fixed.
You can follow all the details in the following thread:
New SmartThings Alexa skill (2020)
There will be an official announcement in that thread once it is fixed. Until then, expect erratic results.