Is there a way to keep my guides locked after a save+close?

Excellent, so my original post was the correct answer?

You could also use a script instead of an action, once installed it would not have the dependency of being loaded as an action does.

// Toggle lock guides

toggleLockedGuides();

function toggleLockedGuides() {
    var idslct = charIDToTypeID("slct");
    var desc6 = new ActionDescriptor();
    var idnull = charIDToTypeID("null");
    var ref1 = new ActionReference();
    var idMn = charIDToTypeID("Mn  "); // Menu item class
    var idMnIt = charIDToTypeID("MnIt"); // Menu item type
    var idTglL = charIDToTypeID("TglL"); // toggleLockGuides
    ref1.putEnumerated(idMn, idMnIt, idTglL);
    desc6.putReference(idnull, ref1);
    executeAction(idslct, desc6, DialogModes.NO);
}

Or this simple one-liner:

app.runMenuItem(charIDToTypeID("TglL"));

or perhaps:

app.runMenuItem(stringIDToTypeID('toggleLockGuides'));

https://prepression.blogspot.com/2017/11/downloading-and-installing-adobe-scripts.html

Is it happening with all the document or only one specific document?