000387 : <value> will lose Ms, since the output is not M enabled

Description

When appending input features containing m-values to a target feature class that is not enabled to store m-values, the input m-values will be lost.

Solution

If you want to preserve m-values, make a copy of the inputs. Alternatively, make a copy of the target dataset, ensuring that the Output Has M values environment setting is set to Enabled.