diff --git a/compiler/src/dotty/tools/dotc/core/TyperState.scala b/compiler/src/dotty/tools/dotc/core/TyperState.scala
index 1204ff121ec7..7eb13df9d829 100644
--- a/compiler/src/dotty/tools/dotc/core/TyperState.scala
+++ b/compiler/src/dotty/tools/dotc/core/TyperState.scala
@@ -119,8 +119,7 @@ class TyperState() {
    *  which is not yet committed, or which does not have a parent.
    */
   def uncommittedAncestor: TyperState =
-    // TODO
-    if (isCommitted) previous.nn.uncommittedAncestor else this
+    if (isCommitted && previous != null) previous.uncheckedNN.uncommittedAncestor else this
 
   /** Commit typer state so that its information is copied into current typer state
    *  In addition (1) the owning state of undetermined or temporarily instantiated
diff --git a/compiler/src/dotty/tools/dotc/core/Types.scala b/compiler/src/dotty/tools/dotc/core/Types.scala
index b068f38dd56d..6eecfb94fd16 100644
--- a/compiler/src/dotty/tools/dotc/core/Types.scala
+++ b/compiler/src/dotty/tools/dotc/core/Types.scala
@@ -2878,6 +2878,7 @@ object Types {
     }
   }
 
+  // `refFn` can be null only if `computed` is true.
   case class LazyRef(private var refFn: (Context => (Type | Null)) | Null) extends UncachedProxyType with ValueType {
     private var myRef: Type | Null = null
     private var computed = false
diff --git a/compiler/src/dotty/tools/dotc/printing/PlainPrinter.scala b/compiler/src/dotty/tools/dotc/printing/PlainPrinter.scala
index d2efbeff2901..d29e096da09e 100644
--- a/compiler/src/dotty/tools/dotc/printing/PlainPrinter.scala
+++ b/compiler/src/dotty/tools/dotc/printing/PlainPrinter.scala
@@ -50,6 +50,9 @@ class PlainPrinter(_ctx: Context) extends Printer {
       tp match {
         case tp: ThisType if tp.cls.is(Package) && !tp.cls.isEffectiveRoot =>
           requiredPackage(tp.cls.fullName).termRef
+        case tp: TypeRef =>
+          val tp1 = tp.dealiasKeepAnnots
+          if tp1 ne tp then homogenize(tp1) else tp
         case tp: TypeVar if tp.isInstantiated =>
           homogenize(tp.instanceOpt)
         case AndType(tp1, tp2) =>
@@ -60,6 +63,8 @@ class PlainPrinter(_ctx: Context) extends Printer {
         if !ctx.mode.is(Mode.Type) && annot.symbol == defn.UncheckedVarianceAnnot =>
           homogenize(parent)
         case tp: SkolemType =>
+          // println(tp.info)
+          // println(tp.info.widen)
           homogenize(tp.info)
         case tp: LazyRef =>
           homogenize(tp.ref)
diff --git a/compiler/src/dotty/tools/dotc/typer/ProtoTypes.scala b/compiler/src/dotty/tools/dotc/typer/ProtoTypes.scala
index fe5c8821288b..b7babdec5ec9 100644
--- a/compiler/src/dotty/tools/dotc/typer/ProtoTypes.scala
+++ b/compiler/src/dotty/tools/dotc/typer/ProtoTypes.scala
@@ -387,10 +387,10 @@ object ProtoTypes {
           case _ =>
             targ = typerFn(arg)
             if ctx.reporter.hasUnreportedErrors then
-              if hasInnerErrors(targ) then
+              if hasInnerErrors(targ.nn) then
                 state.errorArgs += arg
             else
-              state.typedArg = state.typedArg.updated(arg, targ)
+              state.typedArg = state.typedArg.updated(arg, targ.nn)
               state.errorArgs -= arg
         }
       targ.nn