Rates are taking 45-200 seconds to pull or reporting that the ship server returned a 502 error.
If you receive the rates pop-up after a long delay, you will find "Recommended: amazon took X seconds to return rates, you may wish to disable this carrier temporarily."
This appears to be service-related troubles at Amazon for their Merchant Fulfillment services (Amazon Buy Shipping), but we're monitoring closely. You can check the MWS health dashboard to see if they've begun monitoring the situation.
What should I do?
Our first recommendation would be to disable your Amazon buy shipping carrier temporarily. You only need Amazon Buy Shipping for "Seller-Fulfilled Prime" but you may have other reasons to use Amazon Buy Shipping due to the benefits Amazon provides when purchasing their labels.
Otherwise, our second best suggestion is to wait a few seconds and then try to click the rates button once again. Once you have a rate visible, it should be selected in the rates pop-up to prevent a second request from being required when a label is generated.
Have you configured your maximum label price?
If you haven't already, now would be a great time to better restrict your auto-buy limits for labels. These limits prevent SKULabs from suggesting or automatically choosing rates above a set threshold using a per-store domestic/international setting. This setting can be found in the shipping configuration section of each store settings page.
By setting appropriate thresholds here, you can ensure temporary outages at certain providers do not exceed typical thresholds for label purchases. This allows you to ship using whichever method is the cheapest at the time throughout outages at individual providers which is the recommended way to avoid fulfillment downtime during this peak time of the season.
You can always choose a rate that is "Too Expensive" manually in the rates modal for that unusual shipment here and there, but this additional level of protection provides peace of mind for high-pace operations.