Thanks for the info! Turns out we were using npm install instead of npm ci and I suspect that a cache somewhere was effing things up.
Rolled to npm ci, checked the versions used in prod, and it all seems good now.
I no longer have access to an environment where I can reproduce this as we switched to npm ci shortly before your post but well, this seems like the root cause.
Thanks for your lightning-fast reply. Have a nice weekend!