I kept getting 504 - Gateway Timeout errors from the Marriott.com website tonight when searching for hotels. I dropped a note to the Lurker and they got back with me extremely quickly. Sadly she didn't have much to offer other than letting me know she was able to access it, along with the usual suggestions of clearing caches, etc.
She did suggest trying to app, which did work and I was able to search and book through there. Lost out on using TopCashBack by booking that way though.