Transport Variables can not be modified for invoice and shipment mail

Question

I am using magento 2.2.3 and have custom shipping method to magento store,every thing is working fine except custom details to be sent in invoice and shipment mail.Transport variables are modified for order email but not working for invoice and shipment.I have crosschecked and observer is working fine for invoice mail and shipment mail.

Answer 1

Setting of the transport variables was broken for ages. An attempt to fix it was made however the fix did not cover all aspects properly. The failed fix was released in 2.2.4. Please update your magento version to 2.2.5 or latest and issue must be fixed .