with another 80 citations afterwards, one-by-line, but nothing else. As mentioned in the title, the lib.bib file is ~10MB - if I swap this out for a non-existent or tiny bibtex file the problem goes away, and the in-buffer citations are rendered in a red face.
Clearly from this and the below profile the issue is something to do with checking etc the citations for fontification purposes.
## cpu
1,542,884,496 99% - redisplay_internal (C function)
1,542,860,504 99% - jit-lock-function
1,542,860,504 99% - jit-lock-fontify-now
1,542,860,504 99% - jit-lock--run-functions
1,542,860,504 99% - run-hook-wrapped
1,542,860,504 99% - #<compiled 0x19ba3bad288bcf3d>
1,542,860,504 99% - font-lock-fontify-region
1,542,860,504 99% - font-lock-default-fontify-region
1,542,792,728 99% - font-lock-fontify-keywords-region
1,542,661,211 99% - org-cite-activate
1,542,542,267 99% - org-cite-basic-activate
787,037,416 50% - org-cite-basic--get-entry
4,065,194 0% + org-cite-basic--parse-bibliography
754,769,872 48% - org-cite-basic--all-keys
6,151,200 0% + seq-mapcat
3,850,126 0% + org-cite-basic--parse-bibliography
481,332 0% + org-element-interpret-data
129,376 0% + org-cite-basic--print-entry
109,615 0% + org-cite-get-references
87,264 0% org-element-citation-parser
5,988 0% org-activate-links
5,677 0% org-do-emphasis-faces
3,524 0% org-fontify-meta-lines-and-blocks
3,072 0% + org-activate-footnote-links
3,072 0% org-do-latex-and-related
7,392 0% - eval
7,392 0% if
3,072 0% kill-this-buffer-enabled-p
2,112 0% - tool-bar-make-keymap
2,112 0% - tool-bar-make-keymap-1
2,112 0% - mapcar
2,112 0% #<compiled 0x1dd4863a123beee7>
1,176 0% menu-bar-update-buffers
6,219,935 0% + command-execute
1,280 0% + timer-event-handler
24 0% + eldoc-schedule-timer
21 0% + #<compiled -0xa96583997f59b99>
0 0% ...
## memory
5778 95% - redisplay_internal (C function)
5778 95% - jit-lock-function
5778 95% - jit-lock-fontify-now
5778 95% - jit-lock--run-functions
5778 95% - run-hook-wrapped
5778 95% - #<compiled 0x19ba3bad288bcf3d>
5778 95% - font-lock-fontify-region
5778 95% - font-lock-default-fontify-region
5778 95% - font-lock-fontify-keywords-region
5774 95% - org-cite-activate
5762 95% - org-cite-basic-activate
2939 48% - org-cite-basic--get-entry
1631 26% - org-cite-basic--parse-bibliography
400 6% - set-auto-coding
400 6% find-auto-coding
20 0% + org-cite-list-bibliography-files
4 0% + #<compiled -0x1c8cad8ab65dbcdf>
4 0% after-insert-file-set-coding
2819 46% - org-cite-basic--all-keys
1515 25% - org-cite-basic--parse-bibliography
364 6% - set-auto-coding
364 6% find-auto-coding
16 0% - org-cite-list-bibliography-files
8 0% + org-collect-keywords
4 0% #<subr F616e6f6e796d6f75732d6c616d626461_anonymous_lambda_23>
32 0% + seq-mapcat
4 0% + org-cite-basic--print-entry
4 0% org-element-citation-parser
4 0% org-activate-links
233 3% - command-execute
218 3% - byte-code
149 2% + read-extended-command
69 1% - find-file-read-args
69 1% - read-file-name
69 1% - read-file-name-default
15 0% - completing-read-default
1 0% - command-execute
1 0% - funcall-interactively
1 0% - minibuffer-complete
1 0% - completion-in-region
1 0% - completion--in-region
1 0% + #<compiled -0xf4b91251a4f5a2>
15 0% - funcall-interactively
6 0% + find-file
5 0% + execute-extended-command
4 0% scroll-up-command
26 0% + ...
4 0% + timer-event-handler
4 0% + #<compiled -0xa96583997f59b99>