I am having literally this exact situation. I got a shipping notification (Pre-Shipment) on Aug 27th and it hasn't changed since. I contacted them last Tuesday and they asked me to give it a few more days while they look into it. Fast-forward to this week, I contacted them Monday morning and got no response. Sent another message today.
I had this happen once or twice with Mondo and they took care of stuff immediately. They either got back to me or took action super fast. I'm not sure what the problem is but I'm pretty annoyed I've had to fire off 3 messages to them and yet I'm getting constant Mondo merch newsletters each day this week. I hope this isn't a sign of them becoming unreliable... To make things worse, Five Element Ninja lives really close to me, a neighboring zip code, and he got his on-time when it shipped.
The weird thing is we both live in Austin (where Mondo is located) and our packages from them always go from Austin to Dallas and back to Austin. I guess they're just shipping all of their packages to Dallas for distribution, but still, it seems a little silly to do that extra step.