I have a couple of MQTT switches configured with a state topic and optimistic: false.
After I upgraded to 0.36 I could still switch all my switches on but HA didn’t seem to receive the messages on the state topics. Restarting HA did not work.
After a full reboot of my RPi3 it all worked again as expected.
TL;DR: If your MQTT switches don’t work anymore after upgrade to 0.36.x a full device reboot might help.