When there is a connection hiccup (once every couple months) and you get tossed to your backup nick then, in many channels, you can't send. What's worse, you can't re-nick while still in the channel. So you have to /part all such channels, re-nick, then /join them again. Often I just don't bother rejoining. It's extremely frictional.

I literally just re-nicked this week without having to rejoin any channels.

Indeed, i can confirm i have renick-ed without problems.

Maybe you have to kill the ghost of your previous connection if it hasn’t times out yet?

For example, to join #django you have to be a registered user (+r), so you have to learn about NickServ and how it works before even being able to ask a question on a channel.