Not just you that is saying this - ixSystems says the same (if you translate “for a business” into “conservative”): Software Status - TrueNAS Roadmap - Open Source NAS Software
Grub issues sometimes occur when you have some sort of uncertainty between BIOS and the TrueNAS installer and Grub about device order - and this can commonly occur when your BIOS is not set to either “always non-UEFI” or “always UEFI” mode. If you have set BIOS so that it will boot into either you can end up with e.g. installer booting in non-UEFI mode and installed TrueNAS booting in UEFI mode and then things can easily get confused.
So set always UEFI and then reinstall. And hopefully this will not happen.