diff -r d3eb5f50052c -r bf8837e3d7ce mercurial/upgrade_utils/engine.py
--- a/mercurial/upgrade_utils/engine.py	Tue Sep 28 20:00:19 2021 +0200
+++ b/mercurial/upgrade_utils/engine.py	Mon Sep 27 12:09:15 2021 +0200
@@ -638,7 +638,6 @@
         )
 
     assert srcrepo.dirstate._use_dirstate_v2 == (old == b'v2')
-    srcrepo.dirstate._map._use_dirstate_tree = True
     srcrepo.dirstate._map.preload()
     srcrepo.dirstate._use_dirstate_v2 = new == b'v2'
     srcrepo.dirstate._map._use_dirstate_v2 = srcrepo.dirstate._use_dirstate_v2