diff --git a/code/src/java/pcgen/core/Globals.java b/code/src/java/pcgen/core/Globals.java
index 1a044561948..e810c63cf2b 100644
--- a/code/src/java/pcgen/core/Globals.java
+++ b/code/src/java/pcgen/core/Globals.java
@@ -127,7 +127,11 @@ public static Campaign getCampaignKeyed(final String aKey)
 		final Campaign campaign = getCampaignKeyedSilently(aKey);
 		if (campaign == null)
 		{
-			Logging.errorPrint("Could not find campaign: " + aKey);
+			Logging.errorPrint("Could not find campaign: " + aKey
+				+ " - no loaded .pcc file declares CAMPAIGN:" + aKey + "."
+				+ " If this is third-party (non-OGL) data, install the .pcc into the"
+				+ " vendor data dir (" + PCGenSettings.getVendorDataDir()
+				+ ") or homebrew data dir (" + PCGenSettings.getHomebrewDataDir() + ").");
 		}
 
 		return campaign;
diff --git a/code/src/java/pcgen/core/PlayerCharacter.java b/code/src/java/pcgen/core/PlayerCharacter.java
index 54be7e75f8b..802b76a5c3b 100644
--- a/code/src/java/pcgen/core/PlayerCharacter.java
+++ b/code/src/java/pcgen/core/PlayerCharacter.java
@@ -228,6 +228,7 @@
 import pcgen.core.analysis.ChooseActivation;
 import pcgen.core.analysis.DomainApplication;
 import pcgen.core.analysis.RaceUtilities;
+import pcgen.core.analysis.SizeUtilities;
 import pcgen.core.analysis.SkillModifier;
 import pcgen.core.analysis.SkillRankControl;
 import pcgen.core.analysis.SpellCountCalc;
@@ -542,6 +543,20 @@ private PlayerCharacter(PlayerCharacter from)
 	public PlayerCharacter(Collection<Campaign> loadedCampaigns)
 	{
 		LoadContext context = Globals.getContext();
+		// Fail fast on a half-loaded dataset: without a SizeAdjustment flagged
+		// ISDEFAULTSIZE:YES, damage scaling, equipment sizing and the size facet
+		// would all NPE deep in facet wiring.
+		if (SizeUtilities.getDefaultSizeAdjustment() == null)
+		{
+			String gameModeName = SettingsHandler.getGameAsProperty().get().getName();
+			Logging.errorPrint("Game mode '" + gameModeName
+				+ "' has no default size: no SizeAdjustment was loaded with ISDEFAULTSIZE:YES."
+				+ " Sizes are typically defined in a *__sizes.lst file inside the gamemode's"
+				+ " Core Rules data source (e.g. data/pathfinder/.../core_essentials/ce__sizes.lst)."
+				+ " Exactly one size in that file must be flagged ISDEFAULTSIZE:YES.");
+			throw new IllegalStateException("Game mode '" + gameModeName
+				+ "' has no default size. Check earlier log errors for the missing data source.");
+		}
 		id = CharID.getID(context.getDataSetID());
 		AbstractReferenceContext refContext = context.getReferenceContext();
 		controller = refContext.constructNowIfNecessary(CodeControl.class, "Controller");
diff --git a/code/src/java/pcgen/persistence/lst/LstObjectFileLoader.java b/code/src/java/pcgen/persistence/lst/LstObjectFileLoader.java
index d6e6b29f911..7d1ee79147d 100644
--- a/code/src/java/pcgen/persistence/lst/LstObjectFileLoader.java
+++ b/code/src/java/pcgen/persistence/lst/LstObjectFileLoader.java
@@ -27,6 +27,7 @@
 import java.util.List;
 import java.util.Objects;
 import java.util.Observable;
+import java.util.Optional;
 import java.util.Set;
 
 import pcgen.cdom.base.CDOMObject;
@@ -281,7 +282,15 @@ protected void loadLstFile(LoadContext context, CampaignSourceEntry sourceEntry)
 		String aString;
 		try
 		{
-			aString = LstFileLoader.readFromURI(uri).get();
+			// readFromURI returns Optional.empty() when it logs a non-fatal IO/decode error
+			// (e.g. a non-UTF-8 .lst). Skip the file rather than aborting the whole load.
+			Optional<String> read = LstFileLoader.readFromURI(uri);
+			if (read.isEmpty())
+			{
+				setChanged();
+				return;
+			}
+			aString = read.get();
 		}
 		catch (PersistenceLayerException ple)
 		{
diff --git a/code/src/java/pcgen/system/CharacterManager.java b/code/src/java/pcgen/system/CharacterManager.java
index 0232c60a5ab..7556d3a56dd 100644
--- a/code/src/java/pcgen/system/CharacterManager.java
+++ b/code/src/java/pcgen/system/CharacterManager.java
@@ -84,6 +84,14 @@ private CharacterManager()
 	 */
 	public static CharacterFacade createNewCharacter(UIDelegate delegate, DataSetFacade dataset)
 	{
+		if (dataset == null)
+		{
+			Logging.errorPrint("Unable to create character: data sources failed to load (see earlier errors)");
+			delegate.showErrorMessage(LanguageBundle.getString("in_cmCreateErrorTitle"),
+				LanguageBundle.getFormattedString("in_cmCreateErrorMessage",
+					"data sources failed to load - see earlier errors in the log"));
+			return null;
+		}
 		@SuppressWarnings("rawtypes")
 		List campaigns = ListFacades.wrap(dataset.getCampaigns());
 		try
@@ -169,6 +177,14 @@ public static PlayerCharacter openPlayerCharacter(File file, UIDelegate delegate
     private static PlayerCharacter openPcInternal(File file, UIDelegate delegate, DataSetFacade dataset,
 		boolean blockLoadedMessage)
 	{
+		if (dataset == null)
+		{
+			Logging.errorPrint("Unable to load character " + file + ": data sources failed to load (see earlier errors)");
+			delegate.showErrorMessage(LanguageBundle.getString("in_cmLoadErrorTitle"),
+				LanguageBundle.getFormattedString("in_cmLoadErrorMessage",
+					file, "data sources failed to load - see earlier errors in the log"));
+			return null;
+		}
 		@SuppressWarnings("rawtypes")
 		List campaigns = ListFacades.wrap(dataset.getCampaigns());
 		try