我发到FBA的货过了好久才入仓，怎么会这样？

每个人的情况不同吧。有的还是2-3天，有些要更长时间。
进入旺季后情况会更糟，所以要制定相应的计划，及时调整

感觉从7月中旬开始FBA的收货/库存方面就存在问题，我猜应该是亚马逊在建立新的收货系统或者是改善旧的，但是出了一些故障，所以才这么慢

所以每件商品我都会尽量保持在100个单位左右。这样就算收货延迟了也没关系
毕竟现在旺季到了，还是多补点货吧。。

我也觉得挺慢的，问了seller support，他们说，因为进入旺季，FBA的库存量在逐渐增多，所以要花更长的时间来处理货物：
“When shipping products for FBA, inventory that is sent to an Amazon fulfillment center is generally scanned and made available for sale within three business days of delivery. However, since we are coming into peak season with regard to FBA shipments and the volume of FBA shipments is increasing in anticipation of Q4, you will likely see this process take a bit longer. We ask for more days to ensure that shipments are not only received but that any subsequent transshipments are also able to complete processing.”