When "Join on connect" is enabled for an +r channels on irc.freenode.net the channel is denied (you need to be identified), before the identification has been completed. The channel at hand in #blendercoders.

See here an example log

[08:22] [Mode] You have set personal modes: +Ri
[08:22] [Notice] -NickServ- This nickname is registered. Please choose a different nickname, or identify via /msg NickServ identify <password>.
[08:22] [Channel] Cannot join channel (+r) - you need to be identified with services - see https://freenode.net/kb/answer/registration
[08:22] [Notice] -NickServ- You are now identified for ####.

Manual joining afterwards still works. Looks like to start "Join on connect" after identification has been completed should be able to fix the issue.