If my WMR says take action code 1541 but my IRS2go app says it's still being processed? why?

The code 1541 is a generic internal code used by the IRS to identify returns that have been "Delayed". There are different reasons accounting for the 1541 reference number; so not everyone's reason will be the same. ... The most general reason is typically that they have a backlog of returns and are behind on processing. Or, You claimed Earned Income Credit or Additonal Child Tax credit (those were held til mid-Feb before they begin processing)

The IRS expects the earliest EITC/ACTC related refunds to be available in taxpayer bank accounts or debit cards startingFebruary 27, 2019, if these taxpayers chose direct deposit and there are no other issues with their tax return.

but why does it say take action on WMR and says still processing on IRS2go app?

Unless the WMR specifically tells you to call simply wait.

Because the 2 tools are not always in sync.