Slow platform switching since 5.3.4p2

Starting from 5.3.4p2 platform switching become really slow.

Before that switching displayed a "Determining assets that need to be reimported for target platform" dialog, which took a few seconds.

Now all assets seems to get reimported.
This affects even switching between x86 & x64 on Windows, but other platforms are also affected.
We have a large project (>30 GB source assets, >7 GB imported) so it takes minutes even with a cache server.

Tested with 5.3.4f1 (good), 5.3.4p1 (good), 5.3.4p2 (bad), 5.3.4p5 (bad)

Is this a known issue?
If not how to properly report this? (Attaching a 30 GB+ project to the bugreport is obviously not the way...)

 

As it turns out the all asset reimport only happens when using a cache server.
When cache server is off I can still see the hashes being recomputed but there's no reimport after that.

 

I've seen this issue as well, and have had to stop using the cache server for now.