When I activate a scene from an Insteon switch, it works perfectly. When I ask Alexa to execute only some of the actions in the scene ate executed

If you activate the scene from the admin console, does it behave the same as with Alexa?

Likely the answer is yes. Which means your scene links are corrupt. Try restoring all the devices in the scene. If that doesn't work, trying removing the device that isn't responding from the scene and then adding it back in. If that doesn't work, start deleting devices, factory resetting them, adding them back to ISY, then creating the scenes again.

Likely issues with the scene - if ISY gets the command from Alexa, Alexa did its part and triggered. Its up ISY and your switches to react to and execute the scene.

@PapaBear , when you execute a scene from your Insteon switch it will interrogate group members via a group cleanup command to verify that they received/acted on the scene command. If a device did not respond correctly, the switch MAY retry xx times.

When you request a scene to be turned on using Alexa, it communicates to the ISY via a Rest command. The ISY in turn executes the scene. The difference is that when the ISY executes a scene it does NOT interrogate the scene members to see if they received/acted on the command. It assumes the command was received properly.

You likely have poor communication to some of the scene members. The switch uses retries to try to improve communications. The ISY (and Alexa) do not.

You can try to improve communications, or use Individual device On/Off commands (Device on/off vs scene on/off). The ISY will use group cleanups and retries for Device Direct commands.