Here we have two scenarios to observer
1) order created for bundle-product which has value "separately" set for "Ship Bundle Items" field in it's settings : As shown in picture
If we create shipment record for child items via api "POST /V1/shipment/" it creating shipment record but with no data under "Items Shipped" block on shipment record, as shown in screenshot
Also , we are able to create shipment for entire bundle product perfectly , which should not be the case since we have opted "seperatey" for shipping in items settings.
2) order created for bundle-product which has value "together" set for "Ship Bundle Items" field:
The behavior is same here as it happening in scenario 1. Point to be noted here is for bundle product with "together" shipping setting, we should not be able to create shipments record for child items even if it is with blank data for "Items Shipment" record on shipment record.