If you have multiple contexts, this might be the issue:
To create cross-context links in MODX, you must define and configure the site_url and http_host context settings for each individual context rather than relying solely on global system settings. [1, 2]
Yes, these parameters are set in the context.
The cross-context linking was working perfectly, after all.
And suddenly, it stopped working. I assume it has something to do with the update, though that might not necessarily be the case.
I’d check the en context configuration first, especially its context key, status, and base URL. Clearing the MODX cache and rebuilding the context cache would also be worth trying before changing the resource.