nautilus crashes when changing from folder view to list view before the folder contents had time to load.
to reproduce, open a large folder such as /usr/lib.
you need a slow disk. hdds will do. ssds are probably unable to reproduce this.
before the folder contents load, change view to 'list view'.
nautilus crashes.
valgring says:

(nautilus:30477): GLib-GIO-CRITICAL **: g_action_group_has_action: assertion 'G_IS_ACTION_GROUP (action_group)' failed

(nautilus:30477): GLib-GIO-CRITICAL **: g_action_group_get_action_enabled: assertion 'G_IS_ACTION_GROUP (action_group)' failed

(nautilus:30477): GLib-GIO-CRITICAL **: g_action_group_get_action_state: assertion 'G_IS_ACTION_GROUP (action_group)' failed

(nautilus:30477): GLib-CRITICAL **: g_variant_get_type: assertion 'value != NULL' failed

(nautilus:30477): GLib-CRITICAL **: g_variant_type_is_subtype_of: assertion 'g_variant_type_check (type)' failed

(nautilus:30477): GLib-CRITICAL **: g_variant_get_int32: assertion 'g_variant_is_of_type (value, G_VARIANT_TYPE_INT32)' failed

(nautilus:30477): GLib-CRITICAL **: g_variant_unref: assertion 'value != NULL' failed
==30477== Invalid read of size 8
==30477==    at 0x7450321: g_action_map_lookup_action (in /usr/lib/libgio-2.0.so.0.4600.2)
==30477==    by 0x444DAE: real_update_actions_state (nautilus-files-view.c:6169)
==30477==    by 0x435156: nautilus_canvas_view_update_actions_state (nautilus-canvas-view.c:1078)
==30477==    by 0x446A08: nautilus_files_view_update_toolbar_menus (nautilus-files-view.c:6728)
==30477==    by 0x446AC2: done_loading.part.48 (nautilus-files-view.c:3139)
==30477==    by 0x447459: done_loading (nautilus-files-view.c:7118)
==30477==    by 0x447459: nautilus_files_view_stop_loading (nautilus-files-view.c:7212)
==30477==    by 0x447981: nautilus_files_view_destroy (nautilus-files-view.c:2816)
==30477==    by 0x7733014: g_closure_invoke (in /usr/lib/libgobject-2.0.so.0.4600.2)
==30477==    by 0x774557D: ??? (in /usr/lib/libgobject-2.0.so.0.4600.2)
==30477==    by 0x774DDFB: g_signal_emit_valist (in /usr/lib/libgobject-2.0.so.0.4600.2)
==30477==    by 0x774E12E: g_signal_emit (in /usr/lib/libgobject-2.0.so.0.4600.2)
==30477==    by 0x59FCC99: ??? (in /usr/lib/libgtk-3.so.0.1800.6)
==30477==  Address 0x0 is not stack'd, malloc'd or (recently) free'd
==30477== 
==30477== 
==30477== Process terminating with default action of signal 11 (SIGSEGV)
==30477==  Access not within mapped region at address 0x0
==30477==    at 0x7450321: g_action_map_lookup_action (in /usr/lib/libgio-2.0.so.0.4600.2)
==30477==    by 0x444DAE: real_update_actions_state (nautilus-files-view.c:6169)
==30477==    by 0x435156: nautilus_canvas_view_update_actions_state (nautilus-canvas-view.c:1078)
==30477==    by 0x446A08: nautilus_files_view_update_toolbar_menus (nautilus-files-view.c:6728)
==30477==    by 0x446AC2: done_loading.part.48 (nautilus-files-view.c:3139)
==30477==    by 0x447459: done_loading (nautilus-files-view.c:7118)
==30477==    by 0x447459: nautilus_files_view_stop_loading (nautilus-files-view.c:7212)
==30477==    by 0x447981: nautilus_files_view_destroy (nautilus-files-view.c:2816)
==30477==    by 0x7733014: g_closure_invoke (in /usr/lib/libgobject-2.0.so.0.4600.2)
==30477==    by 0x774557D: ??? (in /usr/lib/libgobject-2.0.so.0.4600.2)
==30477==    by 0x774DDFB: g_signal_emit_valist (in /usr/lib/libgobject-2.0.so.0.4600.2)
==30477==    by 0x774E12E: g_signal_emit (in /usr/lib/libgobject-2.0.so.0.4600.2)
==30477==    by 0x59FCC99: ??? (in /usr/lib/libgtk-3.so.0.1800.6)
==30477==  If you believe this happened as a result of a stack
==30477==  overflow in your program's main thread (unlikely but
==30477==  possible), you can try to increase the size of the
==30477==  main thread stack using the --main-stacksize= flag.
==30477==  The main thread stack size used in this run was 8388608.
==30477== 


I'll reinstall gtk/glib with debug symbols later today but I thought I should report what I have so far.
I think this is the only nautilus crash I am seeing in 3.18.4