After upgrading to 2019.4.0, the editor takes 5+ minutes to open (previously < 1 minute on 2019.3.9) with no log output for at least 3-4 minutes. Here's the line in the log before the wait...
" Launched and connected shader compiler UnityShaderCompiler.exe after 0.07 second "
And here's the log after 3-4 minutes...
"
Initializing Unity extensions:...
Editor taking long to open with no log output
" Launched and connected shader compiler UnityShaderCompiler.exe after 0.07 second "
And here's the log after 3-4 minutes...
"
Initializing Unity extensions:...
Editor taking long to open with no log output