User &1 locks &2&3

What causes this issue?

Availability control requests a lock by calling the ENQUEUE function
module ENQUEUE_E_EFMAVCT. This lock cannot be set up because another SAP
transaction is using the lock in question.
Technical information: The C_ENQUEUE routine returned the following
values:
COLLISION_OBJECT = E_EFMAVCT
COLLISION_UNAME = &V1&
The lock object refers to the control object &V2&&V3&.

System Response

The ENQUEUE function module triggers an appropriate exception. If this
exception was not intercepted by the application program, this leads
automatically to the active SAP transaction being cancelled.

How to fix this error?

Look in the lock table to establish which user or transaction is using
the requested lock (<LS>Tools -> Administration -> Monitor -> Lock
entries</>). You may need to contact the user in question.
The lock table entry in question uses the technical object number &V4&
in the lock argument.
Since the ENQUEUE module ENQUEUE_E_EFMAVCT is called with the parameter
_WAIT, you may also try to avoid the observed lock collision by changing
some system parameters (see note 6822).

Error message extract from SAP system. Copyright SAP SE.