For v1:
More than likely the two SKU's are slightly different.  Compare the two SKU's, and make sure there are:
no leading 0's
no spaces
no 0's (zero) that are O's (oh) or I's (eye) that are l's (el) or 1's (one)
If a difference is found, find it on the PO data sheet and change it to match the SKU is in the sales data.
When the change is made click update on the Dashboard and everything should refresh. (you may have to click it twice)
For v2:
This will happen when the name of the item has changed at some point or multiple times. There may also be adjustments descriptions. This is normal due to the way we are finding unique names within sales data.