2018.x batch mode taking far longer for some platforms

My team has been having issues with automated builds taking too long since updating to 2018.x. A quick primer on our build setup is that we have two build machines that handle building our client/server (all are running 2018.2.7f1 at the moment).

• Linux box
  • no cache server
  • responsible for building server executable for linux platform
• Windows box
  • connected to cache server
  • responsible for building windows & macOS clients

The builds are handled via a Jenkins build pipeline with the source checked out via git and there is only ever a single build happening at one time. Each build platform has it's own workspace to prevent library issues.

Since updating to 2018 any time I trigger a macOS build, or a linux server build it takes on average 6 hours to build even if it was simply a code change (old builds are not cleared). If I trigger a build with the same changeset for windows however, it takes a whole 7 minutes to build. Previously this was not the case and all three platforms were relatively consistent in their build times. This is quite perplexing as macOS and linux builds happen on different machines with different configurations (one with and one without the latest cache server).

Our Linux and macOS builds seem to spend the bulk of their time re-importing assets and/or re-crunching textures for some reason even though this happens on a nearly nightly basis. The good majority of our textures are crunched but I think the larger issue is that it is reimporting assets when it shouldn't be. Does anyone have any ideas as to what might be happening or how we might mitigate this issue?

(sample of it crunching...)

Spoiler

Updating Assets/SoL_Resources/Environment/_Basics/Trees/Package2/Red_Delicious_Apple/Red_Delicious_Apple_Desktop_1_Normal.tga - GUID: fe18ea75941760248b2d532a58d0cbaa...
Compressing using quality level 127
crunched in 1.294913
----- Compute hash for Assets/SoL_Resources/Environment/_Basics/Trees/Package2/Red_Delicious_Apple/Red_Delicious_Apple_Desktop_1_Normal.tga.
done. [Time: 1379.525000 ms]
Updating Assets/SoL_Resources/Environment/_Basics/Trees/Package1/White_Oak/Leaf_Map_Maker_Desktop_Fall_Modeler_Use_Only_Atlas_Specular.tga - GUID: fe1c305bb30a8984ea8bc68c448bd58d...
Compressing using quality level 127
crunched in 0.260880