Match 3 Fill Match Gridlock Logic Help

I have a large core of my game already created but am having the most difficult time wrapping my head around the logic to make the game check for matches when creating the board to ensure that the player has matches to start and also to make sure that they don'link textt end up becoming gridlocked. Looking for help to make the logic to reshuffle the board when a gridlock would happen. Linked below is the script i'm using.