Friend List Issues

Well I've been having issues with my friend list for quite some time now. I never really cared too much but it does get annoying. Not exactly sure when it started to glitch itself but it probably started around when I reached 100 friends and decided to delete several people and repeat(half a year ago perhaps?). Well the main issues are that several of the people in my friendlist will be invisible.. as in I can clearly see whenever they are speaking in friendchat/ I appear on their friend list but I can't find their name anywhere whether it be in online or offline. I also can't seem to add some people to my friend list; I've tried several methods to try to "fix" this such as logging out and relogging or deleting and re-adding and only some of which would seem to work.. temporarily usually. There's also the minor issue that I can't delete some people.. I mean they get removed from my friendlist but after relogging they magically reappear.. -_- It's really quite annoying.. so I was wondering if anyone has encountered such issues and if there is any such solutions?