In Editor mode you have to turn off this setting:
Edit > Editor Preferences > General > Performance > Use Less CPU when in background.
In play mode the path to the object changes. Instead of (for example) this:
/Game/EscenaPlayera/M_Playa_WebRemote.M_Playa_WebRemote:PersistentLevel.SpotLuzFarola.LightComponent0
it’s this:
/Game/EscenaPlayera/UEDPIE_0_M_Playa_WebRemote.M_Playa_WebRemote:PersistentLevel.SpotLuzFarola.LightComponent0
UEDPIE_0_ determines the mode, it may change if it’s not “play in editor”.