Mac 10.13.6, InDesign 15.0.1. Repeatable bug. Not related to having any browsers open.

Create new document, can drag guides to page and see them OK. Paste elements on to page, still OK to create guides Adjust margins and columns, still OK.

THEN, adjust Document Setup (for me, adding bleed) and all guides disappear. You can drag a guide from rulers and it looks like it is there, but when you click elsewhere on the screen then that guide disappears.

Please get this sorted. I am sorry to say that this version of InDesign appears to be the buggiest version in quite a while.