ADDITIONAL SYSTEM INFORMATION :
Ubuntu 64,
I download java from repository ppa:linuxuprising/java

A DESCRIPTION OF THE PROBLEM :
javac bxlx/SandBox.java
An exception has occurred in the compiler (11.0.1). Please file a bug against the Java compiler via the Java bug reporting page (http://bugreport.java.com) after checking the Bug Database (http://bugs.java.com) for duplicates. Include your program and the following diagnostic in your report. Thank you.
java.lang.AssertionError: isSubtype UNKNOWN
at jdk.compiler/com.sun.tools.javac.code.Types$4.visitType(Types.java:1123)
at jdk.compiler/com.sun.tools.javac.code.Types$4.visitType(Types.java:1100)
at jdk.compiler/com.sun.tools.javac.code.Type.accept(Type.java:214)
at jdk.compiler/com.sun.tools.javac.code.Types$DefaultTypeVisitor.visit(Types.java:4857)
at jdk.compiler/com.sun.tools.javac.code.Types.isSubtype(Types.java:1096)
at jdk.compiler/com.sun.tools.javac.code.Types.isSubtypeUncheckedInternal(Types.java:1022)
at jdk.compiler/com.sun.tools.javac.code.Types.isSubtypeUnchecked(Types.java:1008)
at jdk.compiler/com.sun.tools.javac.code.Types.isConvertible(Types.java:607)
at jdk.compiler/com.sun.tools.javac.code.Types.isAssignable(Types.java:2319)
at jdk.compiler/com.sun.tools.javac.comp.Check$1.compatible(Check.java:522)
at jdk.compiler/com.sun.tools.javac.comp.Check.checkType(Check.java:563)
at jdk.compiler/com.sun.tools.javac.comp.Check.checkType(Check.java:550)
at jdk.compiler/com.sun.tools.javac.comp.Annotate.attributeAnnotationValues(Annotate.java:459)
at jdk.compiler/com.sun.tools.javac.comp.Annotate.attributeAnnotation(Annotate.java:415)
at jdk.compiler/com.sun.tools.javac.comp.Annotate.annotateNow(Annotate.java:341)
at jdk.compiler/com.sun.tools.javac.comp.Annotate.lambda$annotateLater$0(Annotate.java:267)
at jdk.compiler/com.sun.tools.javac.comp.Annotate.flush(Annotate.java:191)
at jdk.compiler/com.sun.tools.javac.comp.Annotate.unblockAnnotations(Annotate.java:144)
at jdk.compiler/com.sun.tools.javac.comp.TypeEnter.complete(TypeEnter.java:213)
at jdk.compiler/com.sun.tools.javac.code.Symbol.complete(Symbol.java:642)
at jdk.compiler/com.sun.tools.javac.code.Symbol$ClassSymbol.complete(Symbol.java:1326)
at jdk.compiler/com.sun.tools.javac.comp.Attr.visitClassDef(Attr.java:941)
at jdk.compiler/com.sun.tools.javac.tree.JCTree$JCClassDecl.accept(JCTree.java:774)
at jdk.compiler/com.sun.tools.javac.comp.Attr.attribTree(Attr.java:655)
at jdk.compiler/com.sun.tools.javac.comp.Attr.attribStat(Attr.java:724)
at jdk.compiler/com.sun.tools.javac.comp.Attr.visitAnonymousClassDefinition(Attr.java:2397)
at jdk.compiler/com.sun.tools.javac.comp.Attr.lambda$visitAnonymousClassDefinition$2(Attr.java:2355)
at jdk.compiler/com.sun.tools.javac.comp.InferenceContext.notifyChange(InferenceContext.java:265)
at jdk.compiler/com.sun.tools.javac.comp.InferenceContext.notifyChange(InferenceContext.java:256)
at jdk.compiler/com.sun.tools.javac.comp.InferenceContext.lambda$min$5(InferenceContext.java:372)
at jdk.compiler/com.sun.tools.javac.comp.InferenceContext.notifyChange(InferenceContext.java:265)
at jdk.compiler/com.sun.tools.javac.comp.InferenceContext.notifyChange(InferenceContext.java:256)
at jdk.compiler/com.sun.tools.javac.comp.InferenceContext.lambda$dupTo$3(InferenceContext.java:332)
at jdk.compiler/com.sun.tools.javac.comp.InferenceContext.notifyChange(InferenceContext.java:265)
at jdk.compiler/com.sun.tools.javac.comp.InferenceContext.notifyChange(InferenceContext.java:256)
at jdk.compiler/com.sun.tools.javac.comp.Infer.instantiateMethod(Infer.java:242)
at jdk.compiler/com.sun.tools.javac.comp.Resolve.rawInstantiate(Resolve.java:605)
at jdk.compiler/com.sun.tools.javac.comp.Resolve.checkMethod(Resolve.java:644)
at jdk.compiler/com.sun.tools.javac.comp.Attr.checkMethod(Attr.java:4120)
at jdk.compiler/com.sun.tools.javac.comp.Attr.checkIdInternal(Attr.java:3913)
at jdk.compiler/com.sun.tools.javac.comp.Attr.checkMethodIdInternal(Attr.java:3814)
at jdk.compiler/com.sun.tools.javac.comp.Attr.checkId(Attr.java:3803)
at jdk.compiler/com.sun.tools.javac.comp.Attr.visitIdent(Attr.java:3553)
at jdk.compiler/com.sun.tools.javac.tree.JCTree$JCIdent.accept(JCTree.java:2243)
at jdk.compiler/com.sun.tools.javac.comp.Attr.attribTree(Attr.java:655)
at jdk.compiler/com.sun.tools.javac.comp.Attr.visitApply(Attr.java:2006)
at jdk.compiler/com.sun.tools.javac.tree.JCTree$JCMethodInvocation.accept(JCTree.java:1634)
at jdk.compiler/com.sun.tools.javac.comp.Attr.attribTree(Attr.java:655)
at jdk.compiler/com.sun.tools.javac.comp.Attr.attribExpr(Attr.java:702)
at jdk.compiler/com.sun.tools.javac.comp.Attr.visitExec(Attr.java:1773)
at jdk.compiler/com.sun.tools.javac.tree.JCTree$JCExpressionStatement.accept(JCTree.java:1452)
at jdk.compiler/com.sun.tools.javac.comp.Attr.attribTree(Attr.java:655)
at jdk.compiler/com.sun.tools.javac.comp.Attr.attribStat(Attr.java:724)
at jdk.compiler/com.sun.tools.javac.comp.Attr.attribStats(Attr.java:743)
at jdk.compiler/com.sun.tools.javac.comp.Attr.visitBlock(Attr.java:1294)
at jdk.compiler/com.sun.tools.javac.tree.JCTree$JCBlock.accept(JCTree.java:1020)
at jdk.compiler/com.sun.tools.javac.comp.Attr.attribTree(Attr.java:655)
at jdk.compiler/com.sun.tools.javac.comp.Attr.attribStat(Attr.java:724)
at jdk.compiler/com.sun.tools.javac.comp.Attr.visitMethodDef(Attr.java:1098)
at jdk.compiler/com.sun.tools.javac.tree.JCTree$JCMethodDecl.accept(JCTree.java:866)
at jdk.compiler/com.sun.tools.javac.comp.Attr.attribTree(Attr.java:655)
at jdk.compiler/com.sun.tools.javac.comp.Attr.attribStat(Attr.java:724)
at jdk.compiler/com.sun.tools.javac.comp.Attr.attribClassBody(Attr.java:4683)
at jdk.compiler/com.sun.tools.javac.comp.Attr.attribClass(Attr.java:4574)
at jdk.compiler/com.sun.tools.javac.comp.Attr.attribClass(Attr.java:4503)
at jdk.compiler/com.sun.tools.javac.comp.Attr.attrib(Attr.java:4448)
at jdk.compiler/com.sun.tools.javac.main.JavaCompiler.attribute(JavaCompiler.java:1341)
at jdk.compiler/com.sun.tools.javac.main.JavaCompiler.compile(JavaCompiler.java:973)
at jdk.compiler/com.sun.tools.javac.main.Main.compile(Main.java:311)
at jdk.compiler/com.sun.tools.javac.main.Main.compile(Main.java:170)
at jdk.compiler/com.sun.tools.javac.Main.compile(Main.java:57)
at jdk.compiler/com.sun.tools.javac.Main.main(Main.java:43)

STEPS TO FOLLOW TO REPRODUCE THE PROBLEM :
Try to compile bxlx.SandBox source with javac

EXPECTED VERSUS ACTUAL BEHAVIOR :
EXPECTED -
bxlx.SandBox compiles
ACTUAL -
javac throws an exception

---------- BEGIN SOURCE ----------
package bxlx;

public class SandBox {
    
    public interface Callable<T> {
        T call();
    }

    public static <T> T get(Callable<T> c) {
        return null;
    }

    public static void main(String[] args) {
        get(() -> get(new Callable<>() {
            @Override
            public Object call() {
                return get(this);
            }
        }));
    }
}
---------- END SOURCE ----------

CUSTOMER SUBMITTED WORKAROUND :
if the inside callable definition got a specific generic type (new Callable<Object>()), the problem is gone

FREQUENCY : always