I use a small plug by glaphen that this plugin seems to break.  All the plugin does is changes sprite layer priority depending on who is attacking by flipping a switch:

Spriteset_Battle.prototype.battleFieldDepthCompare = function(a, b) {
var priority = BattleManager.getSpritePriority();
if (a._battler && b._battler) {
if (!$gameSwitches.value(500)) {
if (a._battler.isActor() && b._battler.isEnemy()) return 1;
if (a._battler.isEnemy() && b._battler.isActor()) return -1;
} else {
if (a._battler.isActor() && b._battler.isEnemy()) return -1;
if (a._battler.isEnemy() && b._battler.isActor()) return 1;
}
}
if (a.z < b.z) return -1;
if (a.z > b.z) return 1;
if (a.y < b.y) return -1;
if (a.y > b.y) return 1;
return 0;
};

Any chance of a compatibility fix?

What's the exact error you get?

Not sure if this is what you are looking for, but found this in YEP_BattleEngine:

//=============================================================================
// Spriteset_Battle
//=============================================================================

Spriteset_Battle.prototype.isBusy = function() {
    return false;
};

Yanfly.BEC.Spriteset_Battle_update = Spriteset_Battle.prototype.update;
Spriteset_Battle.prototype.update = function() {
    Yanfly.BEC.Spriteset_Battle_update.call(this);
    this.updateZCoordinates();
};

Spriteset_Battle.prototype.updateZCoordinates = function() {
  if (Imported.YEP_ImprovedBattlebacks) {
    this.updateBattlebackGroupRemove();
  } else {
    this._battleField.removeChild(this._back1Sprite);
    this._battleField.removeChild(this._back2Sprite);
  }
  this._battleField.children.sort(this.battleFieldDepthCompare);
  if (Imported.YEP_ImprovedBattlebacks) {
    this.updateBattlebackGroupAdd();
  } else {
    this._battleField.addChildAt(this._back2Sprite, 0);
    this._battleField.addChildAt(this._back1Sprite, 0);
  }
};

Spriteset_Battle.prototype.battleFieldDepthCompare = function(a, b) {
    var priority = BattleManager.getSpritePriority();
    if (a._battler && b._battler && priority !== 0) {
      if (priority === 1) {
        if (a._battler.isActor() && b._battler.isEnemy()) return 1;
        if (a._battler.isEnemy() && b._battler.isActor()) return -1;
      } else if (priority === 2) {
        if (a._battler.isActor() && b._battler.isEnemy()) return -1;
        if (a._battler.isEnemy() && b._battler.isActor()) return 1;
      }
    }
    if (a.z < b.z) return -1;
    if (a.z > b.z) return 1;
    if (a.y < b.y) return -1;
    if (a.y > b.y) return 1;
    return 0;
};

Spriteset_Battle.prototype.isPopupPlaying = function() {
    return this.battlerSprites().some(function(sprite) {
        return sprite.isPopupPlaying();
    });
};

Yanfly.BEC.Spriteset_Battle_battlerSprites =
  Spriteset_Battle.prototype.battlerSprites;
Spriteset_Battle.prototype.battlerSprites = function() {
  var sprites = Yanfly.BEC.Spriteset_Battle_battlerSprites.call(this);
  var length = sprites.length;
  var result = [];
  for (var i = 0; i < length; ++i) {
    var sprite = sprites[i];
    if (!sprite) continue;
    if (!sprite._battler) continue;
    result.push(sprite);
  }
  return result;
};

Try this build: https://www.dropbox.com/s/06iaa12eqvo3odi/dist_20210303.zip?dl=0

updateZCoordinates now only calls the line this._battleField.children.sort(this.battleFieldDepthCompare); without the battleBack stuff, so this might work.

It appears to be working! Thank you so much! Makes me very happy to use this plugin in my project.  I had  an additional question - any terms of use?  I am assuming the backgrounds were ripped from EB?

Yeah the backgrounds that come with the plugin in a separate zip are all ripped from the EB ROM afaik, so try not to use those if publishing.

Feel free to keep me in the loop of any game you develop, whether free or commercial.