CORS headers missing after update to LSWS 5.3.1

We've received a report from a client that CORS headers stopped showing up, following our update to LSWS 5.3.1:
As of today, one of my services is not working any more, because CORS headers don't show up in the server's reply.
After switching back to LSWS 5.3, the CORS headers appeared again.
No further details were provided, but I can ask the client, if necessary to investigate further.
Is this a known issue?