BTW: IIRC, you need sysinstx only when the filesystem has changed. (Not really sure, if this is correct.)
Yes, this should be the case but I've got one time partition not booting and after sysinstx it was ok.
After this error, I issued it after each time I recovered a bootable partition (it is quick to do) and seems not to provide a problems.
I have to correct my latest update about partition aligment !
Finally partition aren't aligned (I used an other calculator but this one rounded results making me think been aligned)
and It seems not possible with ArcaOS to have them aligned on SSD using default driver settings
(I checked under linux using fdisk always providing unaligned partition messages but linux is now able to mount 2 partitions of the 3). I check partition from my older SSD (a 240GB) and first partition was at the same offset

x'7F' not good start offset (If you check your SSD under DFSEE and found under it that first one is at offset x'7F' then, it isn't aligned...
Here is the SSD layout seen under windows7 (msinfo32)
Should AHCI be started with a specific parameter to force use of aligned partition on SSD, I'll check this next...
But first, I have to find out on which adapter this disk is connected to...
(As known, not aligned partition on SSD will increase write operation and this reduces SSD ifetime which is given on a number of write operation)