I've been having a similar experience for many months, but "randomly". I
don't notice the exact wording of Thunderbird's message, but it can take a very
long time (even over an hour) for folders to update, messages to be loaded (even messages
already viewed on previous days and system bootings), and drafts to be auto-saved. I have
more than one "commercial" e-mail account, and this problem occurs in all of
them, but not all at the same time. I don't know where the delay is, or how to
determine that, or how to definitively rule out any candidate. But if the problem occurs
in one account but not another at the same time, that suggests the problem is not my
system.
Bill.