TL;DR: Emojis in Google Chrome bookmarks breaks the Bookmarks plugin.
I realised that Keypirinha had stopped indexing new Google Chrome bookmarks.
As Keypirinha hasn't been updated since 2018/11/14, I suspected that a Google Chrome update had broken the integration so I setup a fresh installation in a VM but it worked fine.
So, as it stood to reason that my problem must be something specific to my usage, I completely reinstalled Google Chrome and Keypirinha but neither made a difference.
It now seemed that the problem was due to my data / configuration.
I researched this general problem and found #55 which led me to the console which reported the following:
09:18:09.160 ** ERROR: Error from Bookmarks.Bookmarks.on_catalog: <class 'UnicodeDecodeError'>: 'charmap' codec can't decode byte 0x81 in position 500790: character maps to
Traceback (most recent call last):
File "C:\Program Files\Keypirinha\default\Packages\Bookmarks.keypirinha-package\bookmarks.py", line 60, in on_catalog
File "C:\Program Files\Keypirinha\default\Packages\Bookmarks.keypirinha-package\providers\chrome.py", line 43, in list_bookmarks
File "C:\Program Files\Keypirinha\default\Packages\Bookmarks.keypirinha-package\providers\chrome.py", line 78, in read_bookmarks
File "lib\json_init.py", line 296, in load
File "lib\encodings\cp1254.py", line 23, in decode