Command:

/execute @e[type=item,name=X] ~ ~ ~ summon armor_stand ~ ~1 ~ entity_spawned AM

This, for some reason, do not work on currenr beta. I can still use the normal summon command, but when I use it with execute command, it just fails. It says something like Failed to summon as (list of entity names, for this case, X multiplied by how many items named X is on the world). This happens when you try execute + summon on command block and chat command.

This problem got to the extent that doing...

/execute @s ~ ~ ~ summon armor_stand ~ ~1 ~ entity_spawned AM

Actually does not work, even if it's equivalent...

/summon armor_stand ~ ~1 ~ entity_spawned AM

does work normally and do not fail.

Since it's not a syntax error, I think something that holds the summon command when used with execute command has something that makes it to not work.

Even though, all other execute commands still work normally. For example, execute + teleport, execute + setblock, execute + effect, etc.