Thunderbolt disk very slow after 10.12.5 update

Hi all,

I have installed the 10.12.5 system update 2 days ago.

After the restart, my external "My Book Thunderbolt duo" RAID-1 array was marked degraded - as usual with Sierra updates. I have waited almost 2 days to see the array online again.

Sadly, the disk I/O are very slow : according to BlackMagic app, no more than 4 MB/s.

The array is connected to thunderbolt 2 cable to my Mac Pro computer. The cable is alone on its bus. I have tried the 3... no changes.

Despite restarts, impossible to get reasonable speed.

I have opened an assistance ticket to Apple.

Anybody in the same situation ? Mac OS stability is really poor now...