Perhaps similar to T198445 but with a slightly different effect. The bullets on the new watchlist show up, but they no longer fill in solid for unseen changes. The timestamp is slightly bolded for the unseen edits, but the bullets remain empty. Note that I disabled any scripts with &safemode=1, so unless a gadget is misbehaving, the problem lies elsewhere. Screenshot of this is below, the red line is where the unseen edits begin.

The green bullets still show up as normal, as can be seen here:

This is happening in Edge on Windows 10. I haven't checked from my home box (Firefox on Debian) yet, and will update if that has the same problem.