Shipping charge not working sometimes? MarketPress

I originally re-opened this thread: https://premium.wpmudev.org/forums/topic/shipping-charge-not-working-sometimes-what-could-be-causing-this But was told to open a new thread.

Same problem. Here's the copy of my post:

"I've had this problem for since the beginning of MarketPress and I already have the Base Zip code filled in the General Settings.

Sporadically it does not calculate shipping charges. My installation is up to date and it's been doing this for the past two years. Recently (in the last week) it's not calculated shipping charges on two orders and it leaves the shipping at $0.00

I'm sure I've brought this up before in the past but it's a continual issue and when searching I found this thread.

This appears to be a bug. I came from using Virtuemart in Joomla and while it was a dog of a software it never not charged shipping. We ship about 20 orders or so every month and there's nothing in common with the addresses or anything.

Please let's get this issue resolved. Thank's in advance and if anyone else is having the same issue, please post in this thread."