In my survival server world in 1.14, I attempted to complete the advancement "Bring Home the Beacon" but upon completing the activity, I was not rewarded the advancement. I killed the wither, made the beacon and then placed in upon a pyramids of blocks. Although the beacon light up, I did not get the advancement. I then created a survival world with cheats enabled to quickly advance to this point in the advancement tree and repeated the steps of summoning the wither, building the beacon and placing it. I did this twice and found the results were the same. Attached is a screenshot one of my two "cheats enabled" tests, as well as a screenshot from my server.