What causes this issue?

You set the release status of Feature Toggle &V1& to "Released: Feature
is rolled out and active in all systems". Therefore it is active by
default in all systems when you release your transport. Existing
customizing regarding the toggle &V1& is not relevant any longer.

System Response

The system issues an error message and will not allow you to continue with this transaction until the error is resolved.

How to fix this error?

You should now also cleanup all code which makes use of the feature
toggle &V1&. Build a "Where-used-list" for the Feature Toggle &V1& and
remove all usages in the code (API of class CL_FEATURE_TOGGLE). Once all
references are deleted you can delete the Feature Toggle itself.
Note: the ATC check 'BC_FTRL' creates by default Prio 2 messages for all
Feature Toggles having the status 'Released'.

Procedure for System Administrators

Error message extract from SAP system. Copyright SAP SE.