System Information
Operating system: Windows 10 Pro
Graphics card: AMD RX580 8G

Blender Version
Broken: 2.83 Master from splash screen latest version
Worked: none of the builds. from 2.79 till 2.83 were consistently bad. It seems to be sort of random

Short description of error

When I go render my smoke sim with fire + smoke or just fire the alpha channel works different in the viewport than in the final render. There is a thread on reddit about this but it doesn't really fix the issue for me. I have found that when I use flame instead of heat for the fire the issue becomes less apparent. Then when I use a set alpha node in the compositor the issue goes away but then there is no alpha channel anymore. When I use another alpha node after that with the alpha pass(?) plugged into it I get the same issue. I have created an workaround for it by making my own alpha channel and then clamping it.

Exact steps for others to reproduce the error See the above.
Based on the default startup or an attached .blend file (as simple as possible).