https://gcc.gnu.org/bugzilla/show_bug.cgi?id=112661
--- Comment #1 from Robin Dapp <rdapp at gcc dot gnu.org> ---
Confirmed, smaller example:
program main
implicit none
integer, parameter :: n=5
character(len=6), dimension(n,n) :: a
character(len=6), dimension(n) :: r1
integer :: i
logical, dimension(n,n) :: mask
write (unit=a,fmt='(I6.6)') (i*i+200-17*i,i=1,n*n)
mask = .true.
forall (i=1:n)
mask(i,i) = .false.
end forall
r1 = maxval(a, dim=1, mask=mask)
end program main
compiled with -O3 -march=rv64gcv_zvl256b