Memory variable revert to an empty string

I have a Memory String tag that has the site name in it.
That memory tag is sometimes going blank, no value, empty string. There is no where anything is writing to that value, we are only reading from it.
Why is this happening, that field is mandatory as we have many Ignition software, one per site. That value goes to nothing in only one site so far and this is version 8.
I now have put the value to read-only to see if this will stop. Is there a way to see who or what wrote to that field?
Is there a reason that the system simply reset that field and I need to know why.

Thanks for any feedback.

The audit system may help you find this, but the correct solution for something that should be a constant is to make an expression tag with the constant.