https://www.pcgamer.com/sea-of-thieves-update/

In a developer update posted today, Rare discussed Sea of Thieves' launch troubles—difficulty connecting and delays receiving in-game rewards top among them—and what they've done so far on the server-side to correct them. The latest set of fixes, however, come by way of a massive client update which constitutes a full redownload of the game: 19.53GB on PC.

The size of the update is a trade-off, says executive producer Joe Neate—it was get these fixes out now, or wait until the patch could be made smaller. "Our ideal scenario was that we got that patchwork done and we released a smaller patch, but we've made the decision to get that full game update [out there] because of all the fixes it's got which is going to improve the experience for everyone," he said, "but it is a full game size update ... you're going to be downloading the client again."