Is the account IMAP or POP?

It is IMAP (hence the allow immediate server notifications setting). I initially thought it might be a server side setting, but that same account does check for new messages successfully one other PC's running the same version of Thunderbird.

Also I never seem to see it hit that account in the lower left status bar on start. Almost like it just doesn't check it. I've also tried setting that "check for new messages on start" to off and unloading, then setting it back - that didn't help.

(thanks for the reply - btw)

So I decided to just delete the account and recreate it. Which I did and even that didn't help. Looks the same, still do not see it try to hit the default account on startup. It is set and will work if I click manually or wait x mins. Still working on other PC's. Very strange.

Found it! Add-on causing it. morelayoutsforthunderbird

http://morelayoutsforthunderbird.mozdev.org/

Disable the add-on and the default account updates on start. Enable the add-on and it stops updating on start.

Good to see you found a solution. We should always look to add-ons first. But that was so specific a problem I doubt I would have ever gone there.

I agree, because it was only affecting the one email account (albeit the default one). But I gave it a shot. I posted the issue to their dev forum, hopefully they will fix. I appreciate you responding to the issue all the same!