gnuplot 5.5 (last modified in 9.18) on centos linux 7.7.1908
information below from valgrind:
==8477== Invalid read of size 1
==8477== at 0x41711D: eval_link_function (axis.c:2412)
==8477== by 0x61DF14: eval_plots (plot2d.c:3313)
==8477== by 0x44BB88: plot_command (command.c:1897)
==8477== by 0x4411AB: command (command.c:659)
==8477== by 0x4411AB: do_line (command.c:429)
==8477== by 0x5CD14B: load_file (misc.c:335)
==8477== by 0x406416: main (plot.c:636)
==8477== Address 0x8c is not stack'd, malloc'd or (recently) free'd
==8477==
==8477==
==8477== Process terminating with default action of signal 11 (SIGSEGV)
==8477== Access not within mapped region at address 0x8C
==8477== at 0x41711D: eval_link_function (axis.c:2412)
==8477== by 0x61DF14: eval_plots (plot2d.c:3313)
==8477== by 0x44BB88: plot_command (command.c:1897)
==8477== by 0x4411AB: command (command.c:659)
==8477== by 0x4411AB: do_line (command.c:429)
==8477== by 0x5CD14B: load_file (misc.c:335)
==8477== by 0x406416: main (plot.c:636)
==8477== If you believe this happened as a result of a stack
==8477== overflow in your program's main thread (unlikely but
==8477== possible), you can try to increase the size of the
==8477== main thread stack using the --main-stacksize= flag.
==8477== The main thread stack size used in this run was 8388608.
==8477==
==8477== HEAP SUMMARY:
==8477== in use at exit: 75,758 bytes in 419 blocks
==8477== total heap usage: 2,030 allocs, 1,611 frees, 7,354,488 bytes allocated
==8477==
==8477== LEAK SUMMARY:
==8477== definitely lost: 0 bytes in 0 blocks
==8477== indirectly lost: 0 bytes in 0 blocks
==8477== possibly lost: 0 bytes in 0 blocks
==8477== still reachable: 75,758 bytes in 419 blocks
==8477== suppressed: 0 bytes in 0 blocks
==8477== Rerun with --leak-check=full to see details of leaked memory
==8477==
==8477== For lists of detected and suppressed errors, rerun with: -s
==8477== ERROR SUMMARY: 1 errors from 1 contexts (suppressed: 0 from 0)
I can't reproduce this.