def jruby_scan_error(string)
  ('a'..'z').to_a.each do |c1|
    ('a'..'z').to_a.each do |c2|
      begin
        # Downcase is necessary to raise the issue
        string.downcase.scan("#{c1}....#{c2}........")
      rescue Exception => e
        puts "c1: #{c1}\tc2: #{c2}\tError: #{e.class}:#{e.message}"
      end
    end
  end
end

jruby_scan_error("abcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyz")
=> nil

jruby_scan_error("abcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyz")

c1: d c2: r Error: Java::JavaLang::ArrayIndexOutOfBoundsException:52
c1: m c2: d Error: Java::JavaLang::ArrayIndexOutOfBoundsException:52
c1: m c2: o Error: Java::JavaLang::ArrayIndexOutOfBoundsException:52
c1: o c2: c Error: Java::JavaLang::ArrayIndexOutOfBoundsException:52
c1: o c2: r Error: Java::JavaLang::ArrayIndexOutOfBoundsException:52
c1: x c2: o Error: Java::JavaLang::ArrayIndexOutOfBoundsException:52

Java::JavaLang::ArrayIndexOutOfBoundsException: 52
	from org.jruby.util.StringSupport.rb_memsearch_qs_utf8_hash(StringSupport.java:2307)
	from org.jruby.util.StringSupport.rb_memsearch_qs_utf8(StringSupport.java:2346)
	from org.jruby.util.StringSupport.memsearch(StringSupport.java:1851)
	from org.jruby.RubyString.strseqIndex(RubyString.java:2757)
	from org.jruby.RubyString.patternSearch(RubyString.java:3881)
	from org.jruby.RubyString.scanOnce(RubyString.java:3841)
	from org.jruby.RubyString.scan19(RubyString.java:3809)
	from org.jruby.RubyString$INVOKER$i$1$0$scan19.call(RubyString$INVOKER$i$1$0$scan19.gen)
	from org.jruby.internal.runtime.methods.JavaMethod$JavaMethodOneOrNBlock.call(JavaMethod.java:384)
	from org.jruby.runtime.callsite.CachingCallSite.cacheAndCall(CachingCallSite.java:338)
	from org.jruby.runtime.callsite.CachingCallSite.call(CachingCallSite.java:163)
	from org.jruby.ir.interpreter.InterpreterEngine.processCall(InterpreterEngine.java:314)
	from org.jruby.ir.interpreter.StartupInterpreterEngine.interpret(StartupInterpreterEngine.java:73)
	from org.jruby.ir.interpreter.Interpreter.INTERPRET_EVAL(Interpreter.java:122)
	from org.jruby.ir.interpreter.Interpreter.evalCommon(Interpreter.java:176)
	from org.jruby.ir.interpreter.Interpreter.evalWithBinding(Interpreter.java:200)
... 160 levels...
	from org.jruby.internal.runtime.methods.JavaMethod$JavaMethodOneOrNBlock.call(JavaMethod.java:384)
	from org.jruby.internal.runtime.methods.AliasMethod.call(AliasMethod.java:61)
	from org.jruby.runtime.callsite.CachingCallSite.cacheAndCall(CachingCallSite.java:338)
	from org.jruby.runtime.callsite.CachingCallSite.call(CachingCallSite.java:163)
	from bin.rails.invokeOther5:require(bin/rails:4)
	from bin.rails.RUBY$script(bin/rails:4)
	from java.lang.invoke.MethodHandle.invokeWithArguments(MethodHandle.java:625)
	from org.jruby.ir.Compiler$1.load(Compiler.java:95)
	from org.jruby.Ruby.runScript(Ruby.java:828)
	from org.jruby.Ruby.runNormally(Ruby.java:747)
	from org.jruby.Ruby.runNormally(Ruby.java:765)
	from org.jruby.Ruby.runFromMain(Ruby.java:578)
	from org.jruby.Main.doRunFromMain(Main.java:417)
	from org.jruby.Main.internalRun(Main.java:305)
	from org.jruby.Main.run(Main.java:232)
	from org.jruby.Main.main(Main.java:204)