Mi rispondo da solo avendo risolto il problema. Se non potete entrare nel client web, potete aggiornare i componenti aggiuntivi attraverso BC administration shell. Di seguito i comandi da lanciare:
Set-NAVAddIn -ServerInstance $NewBcServerInstance -AddinName 'Microsoft.Dynamics.Nav.Client.BusinessChart' -PublicKeyToken 31bf3856ad364e35 -ResourceFile ($AppName = Join-Path $AddinsFolder 'BusinessChart\Microsoft.Dynamics.Nav.Client.BusinessChart.zip')
Set-NAVAddIn -ServerInstance $NewBcServerInstance -AddinName 'Microsoft.Dynamics.Nav.Client.FlowIntegration' -PublicKeyToken 31bf3856ad364e35 -ResourceFile ($AppName = Join-Path $AddinsFolder 'FlowIntegration\Microsoft.Dynamics.Nav.Client.FlowIntegration.zip')
Set-NAVAddIn -ServerInstance $NewBcServerInstance -AddinName 'Microsoft.Dynamics.Nav.Client.OAuthIntegration' -PublicKeyToken 31bf3856ad364e35 -ResourceFile ($AppName = Join-Path $AddinsFolder 'OAuthIntegration\Microsoft.Dynamics.Nav.Client.OAuthIntegration.zip')
Set-NAVAddIn -ServerInstance $NewBcServerInstance -AddinName 'Microsoft.Dynamics.Nav.Client.PageReady' -PublicKeyToken 31bf3856ad364e35 -ResourceFile ($AppName = Join-Path $AddinsFolder 'PageReady\Microsoft.Dynamics.Nav.Client.PageReady.zip')
Set-NAVAddIn -ServerInstance $NewBcServerInstance -AddinName 'Microsoft.Dynamics.Nav.Client.PowerBIManagement' -PublicKeyToken 31bf3856ad364e35 -ResourceFile ($AppName = Join-Path $AddinsFolder 'PowerBIManagement\Microsoft.Dynamics.Nav.Client.PowerBIManagement.zip')
Set-NAVAddIn -ServerInstance $NewBcServerInstance -AddinName 'Microsoft.Dynamics.Nav.Client.RoleCenterSelector' -PublicKeyToken 31bf3856ad364e35 -ResourceFile ($AppName = Join-Path $AddinsFolder 'RoleCenterSelector\Microsoft.Dynamics.Nav.Client.RoleCenterSelector.zip')
Set-NAVAddIn -ServerInstance $NewBcServerInstance -AddinName 'Microsoft.Dynamics.Nav.Client.SatisfactionSurvey' -PublicKeyToken 31bf3856ad364e35 -ResourceFile ($AppName = Join-Path $AddinsFolder 'SatisfactionSurvey\Microsoft.Dynamics.Nav.Client.SatisfactionSurvey.zip')
Set-NAVAddIn -ServerInstance $NewBcServerInstance -AddinName 'Microsoft.Dynamics.Nav.Client.SocialListening' -PublicKeyToken 31bf3856ad364e35 -ResourceFile ($AppName = Join-Path $AddinsFolder 'SocialListening\Microsoft.Dynamics.Nav.Client.SocialListening.zip')
Set-NAVAddIn -ServerInstance $NewBcServerInstance -AddinName 'Microsoft.Dynamics.Nav.Client.VideoPlayer' -PublicKeyToken 31bf3856ad364e35 -ResourceFile ($AppName = Join-Path $AddinsFolder 'VideoPlayer\Microsoft.Dynamics.Nav.Client.VideoPlayer.zip')
Set-NAVAddIn -ServerInstance $NewBcServerInstance -AddinName 'Microsoft.Dynamics.Nav.Client.WebPageViewer' -PublicKeyToken 31bf3856ad364e35 -ResourceFile ($AppName = Join-Path $AddinsFolder 'WebPageViewer\Microsoft.Dynamics.Nav.Client.WebPageViewer.zip')
Set-NAVAddIn -ServerInstance $NewBcServerInstance -AddinName 'Microsoft.Dynamics.Nav.Client.WelcomeWizard' -PublicKeyToken 31bf3856ad364e35 -ResourceFile ($AppName = Join-Path $AddinsFolder 'WelcomeWizard\Microsoft.Dynamics.Nav.Client.WelcomeWizard.zip')
Trovate tutto però al punto 11 del processo di migrazione da BC 14 a BC21 (almeno io stavo facendo questo tipo di migrazione):
learn.microsoft.com/.../upgrade-unmodified-application-v14-v21