I have had a realms account for a couple weeks now, and I have had problems connecting to my realm almost EVERY DAY.  Sometimes I get a "Disconnected from server" while I am on it!  I then lose the last 5-15 minutes of time in the game when it finally errors out.

I had a realms plus account for a month before that, and NEVER HAD A  SINGLE DISCONNECT OR FAILURE TO CONNECT.  Nothing has changed on my side as far as internet or equipment–just going from realms plus to realms.  I don't care about the extra friends (10 vs 2), or the included texture packs--and I am not willing to spend that much regardless, so I went to a regular realms account.  But this is not a free service, I am still PAYING MONEY for this, and I think it is reasonable to at least expect the same reliability and performance.

In looking at other issues, it seems REALMS-9145 is similar.  The OP can't connect to his realm at all, which is not my problem.  But several of the follow-on comments seems to mirror my problem: chronic failures to connect, or disconnects with lost progress...