Update

after/syntax/jsx.vim

@@ -32,12 +32,23 @@ endif
 "   - othree/yajs.vim:              javascriptNoReserved
 
 
+" JSX attributes should color as JS.  Note the trivial end pattern; we let
+" jsBlock take care of ending the region.
+syn region xmlString contained start=+{+ end=++ contains=jsBlock,javascriptBlock
+
+" JSX child blocks behave just like JSX attributes, except that (a) they are
+" syntactically distinct, and (b) they need the syn-extend argument, or else
+" nested XML end-tag patterns may end the outer jsxRegion.
+syn region jsxChild contained start=+{+ end=++ contains=jsBlock,javascriptBlock
+  \ extend
+
 " Highlight JSX regions as XML; recursively match.
 "
 " Note that we prohibit JSX tags from having a < or word character immediately
 " preceding it, to avoid conflicts with, respectively, the left shift operator
 " and generic Flow type annotations (http://flowtype.org/).
-syn region jsxRegion contains=@XMLSyntax,jsxRegion,jsBlock,javascriptBlock
+syn region jsxRegion
+  \ contains=@XMLSyntax,jsxRegion,jsxChild,jsBlock,javascriptBlock
   \ start=+\%(<\|\w\)\@<!<\z([a-zA-Z][a-zA-Z0-9:\-.]*\)+
   \ skip=+<!--\_.\{-}-->+
   \ end=+</\z1\_\s\{-}>+
@@ -45,10 +56,6 @@ syn region jsxRegion contains=@XMLSyntax,jsxRegion,jsBlock,javascriptBlock
   \ keepend
   \ extend
 
-" JSX attributes should color as JS.  Note the trivial end pattern; we let
-" jsBlock take care of ending the region.
-syn region xmlString contained start=+{+ end=++ contains=jsBlock,javascriptBlock
-
 " Add jsxRegion to the lowest-level JS syntax cluster.
 syn cluster jsExpression add=jsxRegion