I have a very simple build plugin that on PostBuild caches two directories and on PreBuild tries to load the two cached directories. However, the cache is always reported as empty on new builds.
Here are two back-to-back builds on the same branch (the second build triggered by a new commit to the branch that added a meaningless comment so as to trigger a cache-friendly build):
I believe this might be related to this bug with caching in deploy previews. We are looking into it and will come back to you as soon as this is fixed.
Thanks for the additional information, this will help us debug this problem!