Make LUA value keeps losing the type
Make Lua value keeps losing the type, requiring a refresh of the node

After refreshing the node I lose the type enum

After a while I am able to refresh the node again and the enum type returns

Sometimes the warning returns and I lose the enum again
This happens every time I start the project, the issue is present in 4.26 (where the screenshots are from, no source modification) and 5.0
I don't think this is a problem with LuaMachine, most likely it's Unreal. That's the only issue I can think which would cause this, because Unreal thinks the struct has changed for some reason. Recompiling the source typically causes this, although it should only happen if you changed the Plugin source.
There are two potential workarounds:
Use the Struct's Constructor method instead of Unreal's "Make (Struct)" operator:

It will automatically set the type for you.
Or check which pins you have visible on the details panel:

I just tried this on a 5.1 project and I'm not able to replicate it. What type of Blueprint are you using? Actor, LuaState, Component?
Can you replicate it with a fresh project? Does it happen with all your blueprints or just a specific one?