Catastrophic I/O error in root pool

Hi,

After several months of not booting my laptop with FreeBSD current (been
using linux off a different part of the same SSD), I attempted to do so
yesterday, only to be confronted with a boot failure and a message about
catastrophic I/O failure in the root pool (exact words may be different,
typing from memory).
Attempts to import the pool while booted from FreeBSD USB stick caused the
system to hang, also with the same message on the console. Importing a
different pool from the other SSD worked.

I then booted linux and ran "dd if=/dev/nvme... of=/dev/null" over the
complete partition w/o a single glitch. (I did NOT attempt to import the
pool here, that's caused a different sort of problem previously)

Finally, I installed and ran smartctl (still on linux), which - although it
doesn't know about my specific device - seemed to indicate "no error".

Any data important to me is on the working pool, so I'm prepared to
overwrite the root pool, unless there's good reason not to (like a simpler
fix for the current situation :-) )

TIA for all and any hints, pointers, advice.
Michael