“There is no active transaction. This error is usually caused by custom plug-ins that ignore errors from service calls and continue processing” is a frequent error generated while attempting to create a new record (Account or Contact in most cases).
This is a bug that you can fix by deactivating the “ActivityFeeds plugin” regarding the entity that generated the error.
First navigate to Customizations then open Sdk Message Processing Steps, select the right plugin and click deactivate
The example given here is the Contact entity. You can follow the same process if you have a similar issue with other entities.