When the user trying to change the name of a default issue link type, for some reason, after a while, it creates a new link type with the same default name.
For example: If you rename the default link type from "Blocks" to "Block", after a while Jira will create a new link type called "Blocks".
- Access Jira > Settings > Issues > Issue Linking
- Rename the "Blocks" to "Block"
NOTE: It can take more than 1 month to recreate the "Blocks"
As Jira provides the option to rename it, it should work and not recreate the default one.
The default link type is being recreated.
Not change or delete the default link type.