No idea, it’s hard to help you without being able to reproduce it 
My Mosquitto updated like yours (2.0.16) and everything’s running fine.
If you try to connect manually to Mosquitto, does it work? (With MQTT X for example)
If you restart Gladys individually, does Gladys reconnect?
If you go into Node-RED, do you see that Node-RED is connected or not?
If you make a new « scenario » in Node-RED or send an MQTT message, does it go through or not?
No secret, in my opinion you have to test each part of the chain to find where it’s getting stuck 
Don’t hesitate to create another thread for that, it’s complicated to understand your issues when everything is mixed together.