rebuild bundle on mac takes 2 hours, while 7 min on windows

i setup a jenkins builder on mac with 4 unity project for each platform,
a few days ago rebuild 4 platform bundle at the same time on mac can be done within 10 minutes.

but now
one platform takes 2 hours, and 3 platform can't be done in 10 hours on mac,
incremental build still take only a few minutes witch is the same as before,
and wired thing is that on windows building bundle for 1 platform can still be done in 10 minutes.

on mac i can see the build bundle progress Dialog title "compiling shader variant" come out lots of times, each time processing the same standard and legacy shaders witch is not used by my asset and not include in my shaderVaraintCollection.

building is fast at first, from some point it becomes very slow

now i still don't know witch assets cause this problem, so no repro can be make to summit a bug.
unity version is 2019.2.11f1

 

i find out why it's so slow on mac, by using instrument time profiler.
it's the progress bar

unity 2019.2.17f1
macOs 10.14.6

batch mode will be ok for jenkins builder, but still a big problem for desktop development