So, really not sure why, but I just slightly adjusted the size of the region (left out the “-” in front of the amount) and then it started to recognize. Expanded the region back to original size and it stopped recognizing. Then I typed out the amount (with the “-”) into the field and it started recognizing consistently. Has worked successfully for several invoices now.
Not sure how that field got untrained, but this is resolved (and was done so fairly quickly haha)