Very slow boot ReadKernelCache

I'm experience a terrible issue with the latest update of High Sierra. I have a Mac Pro (Late 2013). The upgrade was smooth. I have external Drobo drives (3 of them, 1 mini and 2 5D), all connected via Thunderbolt. Also have 2 monitors (LG and ASUS), connected as well via Thunderbolt. After the security supplement update, the Drobo stop mounting. I tried everything!! Including updates of Drobo manager with no success. At the same time, the Mac Pro started to boot VERY SLOWLY. I mean 7 minutes without anything connected, and it just doesn't start if I connect the Drobos (turned off!).

I took every possible step (NVRAM, SRAM) with no success. If I try command-R, it doesn't work. Re-installed High Sierra with no change.

Finally I was able to start in Verbose mode and see that the startup process takes like 2 minutes to start and then I noticed it stops after "Start ReadKernelCache" and "Star UncompressKernelCache". More than 1 minute on each. After that it goes fast!

After it starts (without Drobo connected) it works fine! Very fast and reliable. I ran EtreCheck with excellent results!

Is there anything I can do to avoid a full format and re-install? What is happening when Kernel issues take that long?

Any help will be appreciated !