Index: binaries/data/mods/public/simulation/components/Trainer.js
===================================================================
--- binaries/data/mods/public/simulation/components/Trainer.js
+++ binaries/data/mods/public/simulation/components/Trainer.js
@@ -624,7 +624,10 @@
  */
 Trainer.prototype.StopBatch = function(id)
 {
-	this.queue.get(id).Stop();
+	const item = this.queue.get(id);
+	if (!item)
+		return;
+	item.Stop();
 	this.queue.delete(id);
 };
 
@@ -663,6 +666,8 @@
 Trainer.prototype.Progress = function(id, allocatedTime)
 {
 	const item = this.queue.get(id);
+	if (!item)
+		return 0;
 	const usedTime = item.Progress(allocatedTime);
 	if (item.IsFinished())
 		this.queue.delete(id);
Index: binaries/data/mods/public/simulation/components/tests/test_Production.js
===================================================================
--- /dev/null
+++ binaries/data/mods/public/simulation/components/tests/test_Production.js
@@ -0,0 +1,140 @@
+Engine.RegisterGlobal("Resources", {
+	"BuildSchema": (a, b) => {},
+	"GetCodes": () => ["food"]
+});
+Engine.LoadHelperScript("Player.js");
+Engine.LoadHelperScript("Sound.js");
+Engine.LoadHelperScript("Transform.js");
+Engine.LoadComponentScript("interfaces/BuildRestrictions.js");
+Engine.LoadComponentScript("interfaces/EntityLimits.js");
+Engine.LoadComponentScript("interfaces/Foundation.js");
+Engine.LoadComponentScript("interfaces/ProductionQueue.js");
+Engine.LoadComponentScript("interfaces/Researcher.js");
+Engine.LoadComponentScript("interfaces/StatisticsTracker.js");
+Engine.LoadComponentScript("interfaces/TechnologyManager.js");
+Engine.LoadComponentScript("interfaces/Timer.js");
+Engine.LoadComponentScript("interfaces/Trainer.js");
+Engine.LoadComponentScript("interfaces/TrainingRestrictions.js");
+Engine.LoadComponentScript("interfaces/Trigger.js");
+Engine.LoadComponentScript("interfaces/Upgrade.js");
+Engine.LoadComponentScript("EntityLimits.js");
+Engine.LoadComponentScript("ProductionQueue.js");
+Engine.LoadComponentScript("Researcher.js");
+Engine.LoadComponentScript("TechnologyManager.js");
+Engine.LoadComponentScript("Trainer.js");
+Engine.LoadComponentScript("TrainingRestrictions.js");
+
+Engine.RegisterGlobal("ApplyValueModificationsToEntity", (_, value) => value);
+Engine.RegisterGlobal("ApplyValueModificationsToTemplate", (_, value) => value);
+
+AddMock(SYSTEM_ENTITY, IID_Timer, {
+	"CancelTimer": (id) => {},
+	"SetInterval": (ent, iid, func) => 1
+});
+
+AddMock(SYSTEM_ENTITY, IID_Trigger, {
+	"CallEvent": () => {}
+});
+
+const playerID = 1;
+const playerEntityID = 11;
+const entityID = 21;
+
+const template = {
+	"Cost": { "BuildTime": 1000 }
+};
+
+AddMock(SYSTEM_ENTITY, IID_TemplateManager, {
+	"TemplateExists": () => true,
+	"GetTemplate": name => (template)
+});
+
+let cmpTrainer = ConstructComponent(entityID, "Trainer", {
+        "Entities": { "_string": "units/{civ}/cavalry_javelineer_b " +
+                                 "units/{native}/support_female_citizen" }
+});
+cmpTrainer.GetUpgradedTemplate = (template) => template;
+
+AddMock(SYSTEM_ENTITY, IID_PlayerManager, {
+	"GetPlayerByID": id => playerEntityID
+});
+
+AddMock(playerEntityID, IID_Player, {
+	"GetDisabledTechnologies": () => {},
+	"GetDisabledTemplates": () => ({}),
+	"GetPlayerID": () => playerID,
+	"RefundResources": () => {},
+	"TryReservePopulationSlots": () => false,
+	"TrySubtractResources": () => true,
+	"UnReservePopulationSlots": () => {},
+	"UnBlockTraining": () => {},
+});
+
+AddMock(playerEntityID, IID_Identity, {
+	"GetCiv": () => "iber",
+});
+
+AddMock(entityID, IID_Ownership, {
+	"GetOwner": () => playerID
+});
+
+AddMock(entityID, IID_Identity, {
+	"GetCiv": () => "iber"
+});
+
+cmpTrainer.OnOwnershipChanged({ "to": playerID });
+
+let cmpResearcher = ConstructComponent(entityID, "Researcher", {
+	"Technologies": {
+		"_string": "technologies/{civ}/will"
+	}
+});
+let cmpProductionQueue = ConstructComponent(entityID, "ProductionQueue", null);
+
+TS_ASSERT(cmpProductionQueue.AddItem("units/iber/cavalry_javelineer_b", "unit", 1));
+TS_ASSERT_EQUALS(cmpProductionQueue.GetQueue().length, 1);
+cmpProductionQueue.ProgressTimeout(null, 500);
+
+Engine.RegisterGlobal("TechnologyTemplates", {
+	"GetAll": () => [],
+	"Get": (tech) => {
+		return template;
+	},
+	"Has": () => true,
+});
+ConstructComponent(playerEntityID, "TechnologyManager", null);
+
+AddMock(SYSTEM_ENTITY, IID_GuiInterface, {
+	"SetSelectionDirty": () => {}
+});
+
+cmpProductionQueue.RemoveItem(cmpProductionQueue.nextID - 1);
+TS_ASSERT(cmpProductionQueue.AddItem("technologies/iber/will", "technology"));
+
+cmpProductionQueue.RemoveItem(cmpProductionQueue.nextID - 1);
+
+
+// #6763 (If the item is removed in cmpTrainer, don't error in cmpProductionQueue.)
+TS_ASSERT(cmpProductionQueue.AddItem("units/iber/cavalry_javelineer_b", "unit", 1));
+
+AddMock(SYSTEM_ENTITY, IID_TemplateManager, {
+	"TemplateExists": () => false,
+	"GetTemplate": name => (template)
+});
+
+cmpTrainer.OnValueModification({ "component": "Promotion", "entities": [entityID] });
+cmpProductionQueue.OnOwnershipChanged({ "to": INVALID_PLAYER });
+
+AddMock(SYSTEM_ENTITY, IID_TemplateManager, {
+	"TemplateExists": () => true,
+	"GetTemplate": name => (template)
+});
+cmpTrainer.CalculateEntitiesMap();
+TS_ASSERT(cmpProductionQueue.AddItem("units/iber/cavalry_javelineer_b", "unit", 1));
+
+AddMock(SYSTEM_ENTITY, IID_TemplateManager, {
+	"TemplateExists": () => false,
+	"GetTemplate": name => (template)
+});
+cmpTrainer.OnValueModification({ "component": "Promotion", "entities": [entityID] });
+cmpProductionQueue.ProgressTimeout(null, 500);