I too use my computer to do the check-in. On my upcoming cruise this end of August at exactly 45 days out I logged in to my account opened the particular sailing and check in was available. Did my check in got to pick check in time, set up account etc. Cruise Documents became available exactly 30 days out at which time I printed my bag tags off the last page.
I do have the app but have not used it to date. Will use it on the day for health info and safety drill viewing and confirmation of same.
Its so strange how common it is with RCL some basic things work for some and not for others. Hopefully one day there IT department gets all its ducks in a row.