Teachme1971,
Welcome to the forum!
I use gDMSS Plus on my Android phone. Twice in 10 months the Push Notifications have stopped working. Both times it was that Push Notifications got disabled somehow.
I had to re-enable Push, then the problem went away.
Steps for me:
Main Screen, choose "Alarm Manager"
"Push Config"
Select your NVR
Move the slide switch at top of screen
Note: Push Type I use is "Live Preview"
Also, the IVS settings were erased. I had to re=enable the IVS type (Cross Region, Cross Line, etc)
And then I had to re-define which cameras to use.
A mystery, at least to me.
Fastb