Gnus frequently hangs at "nnimap read 0k from imap.gmail.com"

[Tassilo Horn <tsdh@gnu.org>]

Hi all,

since about one or two months, Gnus frequently hangs when retrieving new
mail from Gmail.  I use demons checking for new mail every few minutes
of idle time.

--8<---------------cut here---------------start------------->8---
(add-to-list 'gnus-secondary-select-methods
	     '(nnimap "Gmail"
		      (nnimap-address "imap.gmail.com")))

(require 'gnus-demon)
(gnus-demon-add-handler 'gnus-demon-scan-news 15 5)
--8<---------------cut here---------------end--------------->8---

When Gnus hangs, *Messages* shows:

  20130625T141848.814> nnimap read 0k from imap.gmail.com

I can easily hit `C-g' to quit, and then a `g' will usually work fine
again.  I also use two other IMAP accounts, but this problem seems to
occur only with Gmail.

Is there anyone else encountering this problem?  And how can I diagnose
what's the culprit?

After such a hang, I've checked the " *nnimap imap.gmail.com nil
*nntpd**" buffer.  It contained

--8<---------------cut here---------------start------------->8---
...
* 1201 FETCH (UID 2637 FLAGS (%Seen))
* 1202 FETCH (UID 2638 FLAGS (%Seen))
* 1203 FETCH (UID 2640 FLAGS (%Seen))
2498 OK Success
--8<---------------cut here---------------end--------------->8---

which doesn't look as if it stalled during doing IMAP stuff, so I guess
the problem is somewhere in initiating a connection to Gmail...

Bye,
Tassilo