To give more information :

The bug seen (RAID1 GUI sticky in Initializing state) is encountered while re-installing FreeNAS and re-create RAID1 but keeping disk content (iow, the Format disk step of a clean install from scratch are voluntarily not executed here in order to keep/retreive previous install disk content).

The procedures works (disk content can be retreived), but GUI for RAID1 seems trubled and is sticky in Initialising state instead of expected Complete.

1 - Add both disks in Disks|Management but declare them as SofRAID as they were previously fomated like this.
2- Re-create the RAID1 configuration :
The RAID1 is sticky in Initializing whereas it has been successfuly re-created in the information tab.
3 -Re-create the mount point
The previous RAID1 content is now readable : previous files are all present.

Hope these new information can help to understand the way RAID1 GUI comes sticky.

BR