Ensure Absolute Grid and Set Grid value

It seems to work fine on my system. I did notice that the script doesn't check if the Edit window grid is set to Bars|Beats so I added a couple of lines to ensure that it is. That might be why it fails for you.
I also added comments for the whole script.

//Define grid mode button
var gridBtn = sf.ui.proTools.mainWindow.editModeCluster.gridModeButton.invalidate();

//Get state of Grid mode button (is it set to aabsolute?)
var isAbsolute = gridBtn.title.invalidate().value.indexOf("Absolute") === 0;

// Check if grid mode is selected (by checking if any other mode is checked) and select it if it isn't
var isSelected = ![
    sf.ui.proTools.mainWindow.editModeCluster.slipModeButton,
    sf.ui.proTools.mainWindow.editModeCluster.shuffleModeButton,
    sf.ui.proTools.mainWindow.editModeCluster.spotModeButton,
].some(btn => btn.value.invalidate().value === 'Selected');

if (!isSelected) gridBtn.elementClick();

// If Absolute Grid mode is not selected click grid mode button again to switch it from Relative mode
if (!isAbsolute) { gridBtn.elementClick(); }

// Make sure Edit window grid is set to Bars|Beats
sf.ui.proTools.gridSet({
    gridValueName: "Bars|Beats",
});

//Set edit grid to 1 bar
sf.ui.proTools.gridSet({
    gridValueName: "1 bar",
});