here is the backtrace from an identical hang with a different article in the same group:
2017-08-22 14:10:48.609113-0400 emacs[16623:7011753] [general] Connection to 'pboard' server had an error: <error: 0x7fffb7597ca0> { count = 1, transaction: 0, voucher = 0x0, contents =
"XPCErrorDescription" => <string: 0x7fffb7597f18> { length = 18, contents = "Connection invalid" }
}
2017-08-22 14:11:02.771791-0400 emacs[16623:7011721] Detected potentially harmful notification post rate of 229.322 notifications per second
2017-08-22 14:11:12.773714-0400 emacs[16623:7011721] Detected potentially harmful notification post rate of 300.907 notifications per second
2017-08-22 14:11:22.774338-0400 emacs[16623:7011721] Detected potentially harmful notification post rate of 280.44 notifications per second
2017-08-22 14:11:32.774777-0400 emacs[16623:7011721] Detected potentially harmful notification post rate of 290.527 notifications per second
emacs was compiled with optimization - stepping may behave oddly; variables may not be available.
Process 16623 stopped
* thread #1, queue = 'com.apple.main-thread', stop reason = signal SIGSTOP
frame #0: 0x00000001001a4de9 emacs`lookup_image [inlined] search_image_cache(f=0x000000010305afa8, spec=4358862915, hash=4195912884339560560) at image.c:1454 [opt]
1451
1452 for (img = c->buckets[i]; img; img = img->next)
1453 if (img->hash == hash
-> 1454 && !NILP (Fequal (img->spec, spec))
1455 && img->frame_foreground == FRAME_FOREGROUND_PIXEL (f)
1456 && img->frame_background == FRAME_BACKGROUND_PIXEL (f))
1457 break;
(lldb) bt
* thread #1, queue = 'com.apple.main-thread', stop reason = signal SIGSTOP
* frame #0: 0x00000001001a4de9 emacs`lookup_image [inlined] search_image_cache(f=0x000000010305afa8, spec=4358862915, hash=4195912884339560560) at image.c:1454 [opt]
frame #1: 0x00000001001a4d82 emacs`lookup_image(f=0x000000010305afa8, spec=4358862915) at image.c:1739 [opt]
frame #2: 0x0000000100044a68 emacs`handle_single_display_spec(it=<unavailable>, spec=<unavailable>, object=<unavailable>, overlay=<unavailable>, position=<unavailable>, bufpos=<unavailable>, display_replaced=<unavailable>, frame_window_p=<unavailable>) at xdisp.c:5299 [opt]
frame #3: 0x000000010001dd85 emacs`handle_display_spec(it=0x00007fff5fbf8280, spec=4358862915, object=4523100261, overlay=0, position=0x00007fff5fbf83b8, bufpos=1765, frame_window_p=<unavailable>) at xdisp.c:4800 [opt]
frame #4: 0x00000001000452e1 emacs`handle_display_prop(it=0x00007fff5fbf8280) at xdisp.c:4719 [opt]
frame #5: 0x000000010004544b emacs`handle_stop(it=0x00007fff5fbf8280) at xdisp.c:3425 [opt]
frame #6: 0x0000000100048434 emacs`next_element_from_buffer(it=0x00007fff5fbf8280) at xdisp.c:8398 [opt]
frame #7: 0x000000010001c6c2 emacs`get_next_display_element(it=0x00007fff5fbf8280) at xdisp.c:6992 [opt]
frame #8: 0x000000010002ab68 emacs`display_line(it=0x00007fff5fbf8280, cursor_vpos=<unavailable>) at xdisp.c:21318 [opt]
frame #9: 0x000000010002a508 emacs`try_window(window=<unavailable>, pos=(charpos = 921, bytepos = 921), flags=<unavailable>) at xdisp.c:17573 [opt]
frame #10: 0x000000010004f8e0 emacs`redisplay_window(window=4356634629, just_this_one_p=<unavailable>) at xdisp.c:17020 [opt]
frame #11: 0x000000010004db36 emacs`redisplay_window_0(window=<unavailable>) at xdisp.c:14780 [opt] frame #12: 0x0000000100136e86 emacs`internal_condition_case_1(bfun=(emacs`redisplay_window_0 at xdisp.c:14779), arg=4356634629, handlers=<unavailable>, hfun=(emacs`redisplay_window_error at xdisp.c:14771)) at eval.c:1347 [opt]
frame #13: 0x000000010004d19d emacs`redisplay_windows(window=<unavailable>) at xdisp.c:14760 [opt]
frame #14: 0x000000010004d164 emacs`redisplay_windows(window=<unavailable>) at xdisp.c:14754 [opt]
frame #15: 0x00000001000282af emacs`redisplay_internal at xdisp.c:14249 [opt]
frame #16: 0x00000001000bf92e emacs`read_char(commandflag=1, map=4351707683, prev_event=0, used_mouse_menu=0x00007fff5fbfeabf, end_time=0x0000000000000000) at keyboard.c:2484 [opt]
frame #17: 0x00000001000bd40a emacs`read_key_sequence(keybuf=<unavailable>, bufsize=30, prompt=<unavailable>, dont_downcase_last=<unavailable>, can_return_switch_frame=<unavailable>, fix_current_buffer=<unavailable>, prevent_redisplay=<unavailable>) at keyboard.c:9151 [opt]
frame #18: 0x00000001000bbc02 emacs`command_loop_1 at keyboard.c:1372 [opt]
frame #19: 0x0000000100136e12 emacs`internal_condition_case(bfun=(emacs`command_loop_1 at keyboard.c:1263), handlers=<unavailable>, hfun=(emacs`cmd_error at keyboard.c:942)) at eval.c:1323 [opt]
frame #20: 0x00000001000ca800 emacs`command_loop_2(ignore=<unavailable>) at keyboard.c:1114 [opt]
frame #21: 0x00000001001366b9 emacs`internal_catch(tag=<unavailable>, func=(emacs`command_loop_2 at keyboard.c:1110), arg=0) at eval.c:1088 [opt]
frame #22: 0x00000001000bae5e emacs`command_loop at keyboard.c:1093 [opt]
frame #23: 0x00000001000bad6f emacs`recursive_edit_1 at keyboard.c:699 [opt]
frame #24: 0x00000001000bafa3 emacs`Frecursive_edit at keyboard.c:770 [opt]
frame #25: 0x00000001000b9bb7 emacs`main(argc=0, argv=<unavailable>) at emacs.c:1706 [opt]
frame #26: 0x00007fffae679235 libdyld.dylib`start + 1
frame #27: 0x00007fffae679235 libdyld.dylib`start + 1