I experience the exact same bug, in that the backtrace looks identical.

Similar to the original reporter, it occurs while completing symbols for Rust, and my setup also involves Corfu. It does not happen on every complete, but usually within 10 minutes of development.

But some differences are probably important: my setup is with eglot, not lsp-mode, and I do not use Cape.

Maybe it is relevant that the trace ending with the failing Fget starts with jsonrpc. Is there a way to monitor the exact communication emacs has with the language server?

* Backtrace (snippet):

Thread 1 (Thread 0x7ffff2837080 (LWP 150113) "emacs"):
#0  Fget (symbol=0x5555564e3dc0, propname=0x66f0) at /usr/src/debug/emacs/emacs-29.4-wayland/src/lisp.h:1152
        propval = <optimized out>
        propval = <optimized out>
#1  Fget (symbol=0x5555564e3dc0, propname=0x66f0) at /usr/src/debug/emacs/emacs-29.4-wayland/src/fns.c:2516
        propval = <optimized out>
#2  0x0000555555681201 in parse_modifiers (symbol=0x5555564e3dc0) at /usr/src/debug/emacs/emacs-29.4-wayland/src/keyboard.c:6897
        elements = <optimized out>
        elements = <optimized out>
        end = <optimized out>
        modifiers = <optimized out>
        unmodified = <optimized out>
        mask = <optimized out>
#3  parse_modifiers (symbol=0x5555564e3dc0) at /usr/src/debug/emacs/emacs-29.4-wayland/src/keyboard.c:6888
        elements = <optimized out>
        end = <optimized out>
        modifiers = <optimized out>
        unmodified = <optimized out>
        mask = <optimized out>
#4  0x000055555568e7c8 in reorder_modifiers (symbol=<optimized out>) at /usr/src/debug/emacs/emacs-29.4-wayland/src/keyboard.c:7028
        parsed = <optimized out>
        parsed = <optimized out>
#5  access_keymap_1 (map=0x7fffefe131b3, idx=<optimized out>, t_ok=false, noinherit=false, autoload=true) at /usr/src/debug/emacs/emacs-29.4-wayland/src/keymap.c:342
No locals.
#6  0x000055555567d16b in access_keymap (noinherit=false, autoload=true, map=<optimized out>, idx=<optimized out>, t_ok=false) at /usr/src/debug/emacs/emacs-29.4-wayland/src/keymap.c:496
        val = <optimized out>
        val = <optimized out>
#7  read_char (commandflag=0, map=0x0, prev_event=0x0, used_mouse_menu=0x0, end_time=0x7fffffffb5b0) at /usr/src/debug/emacs/emacs-29.4-wayland/src/keyboard.c:3018
        c = <optimized out>
        local_getcjmp = {{__jmpbuf = {93825000405056, -5147324661749537557, 1, 4611686019484352512, 5, 0, -5147324661946669845, -1313834696378178325}, __mask_was_saved = 0, __saved_mask = {__val = {0, 93825010269488, 93825104789632, 140737488335792, 18446744073709550936, 11, 93825104789616, 140737488335856, 140737279378894, 140737488335856, 140737488335920, 0, 140737488335920, 0, 93825010269488, 140737488336000}}}}
        save_jump = {{__jmpbuf = {12048, 140737188459256, 140737488335856, 93825095637120, 16, -7692597586030666240, 48, 1}, __mask_was_saved = 1453957408, __saved_mask = {__val = {140737488335776, 2, 140737488335824, 140737488335760, 140737321006214, 1, 140737321006651, 14319535557742690304, 6, 140737488335696, 140737279373914, 93825000331312, 0, 1, 1, 93823560581122}}}}
        tem = <optimized out>
        save = 0x0
        previous_echo_area_message = 0x0
        also_record = 0x0
        reread = false
        recorded = false
        polling_stopped_here = false
        orig_kboard = 0x5555564e3dc0
        retry = <optimized out>
        jmpcount = <optimized out>
#8  0x0000555555742662 in read_filtered_event (no_switch_frame=false, ascii_required=false, error_nonascii=false, input_method=<optimized out>, seconds=0x7a) at /usr/src/debug/emacs/emacs-29.4-wayland/src/lread.c:702
        val = <optimized out>
        delayed_switch_frame = <optimized out>
        end_time = {tv_sec = 1723636772, tv_nsec = 958651372}
        retry = <optimized out>
#9  0x00007fffef3c3337 in F7369742d666f72_sit_for_0 () from /usr/bin/../lib/emacs/29.4/native-lisp/29.4-ebb0abfe/preloaded/subr-13adf6a6-bfb9f448.eln
No symbol table info available.
#10 0x000055555571364d in Ffuncall (nargs=2, args=0x7fffffffb718) at /usr/src/debug/emacs/emacs-29.4-wayland/src/eval.c:2999
        count = <optimized out>
        val = <optimized out>
#11 0x00007fffce347844 in F6a736f6e7270632d72657175657374_jsonrpc_request_0 () from /usr/lib/emacs/29.4/native-lisp/29.4-ebb0abfe/jsonrpc-e62a9c36-62ae7160.eln
No symbol table info available.


--
Sigve Indregard