Partial fix perhaps?

common/lib/xmodule/xmodule/library_tools.py

@@ -4,6 +4,7 @@ XBlock runtime services for LibraryContentModule
 from django.core.exceptions import PermissionDenied
 from opaque_keys.edx.locator import LibraryLocator
 from xmodule.library_content_module import ANY_CAPA_TYPE_VALUE
+from xmodule.modulestore import ModuleStoreEnum
 from xmodule.modulestore.exceptions import ItemNotFoundError
 from xmodule.capa_module import CapaDescriptor
 
@@ -125,7 +126,9 @@ class LibraryToolsService(object):
             return
 
         source_blocks = []
-        library_key = dest_block.source_library_key.for_version(version)
+        library_key = dest_block.source_library_key
+        if version:
+            library_key = library_key.replace(branch=ModuleStoreEnum.BranchName.library, version_guid=version)
         library = self._get_library(library_key)
         if library is None:
             raise ValueError("Requested library not found.")

common/lib/xmodule/xmodule/modulestore/split_mongo/split.py

@@ -2205,7 +2205,7 @@ class SplitMongoModuleStore(SplitBulkWriteMixin, ModuleStoreWriteBase):
         # so that we can access descendant information quickly
         source_structures = {}
         for key in source_keys:
-            course_key = key.course_key.for_version(None)
+            course_key = key.course_key
             if course_key.branch is None:
                 raise ItemNotFoundError("branch is required for all source keys when using copy_from_template")
             if course_key not in source_structures:
@@ -2264,9 +2264,9 @@ class SplitMongoModuleStore(SplitBulkWriteMixin, ModuleStoreWriteBase):
         new_children = list()  # ordered list of the new children of new_parent_block_key
 
         for usage_key in source_keys:
-            src_course_key = usage_key.course_key.for_version(None)
+            src_course_key = usage_key.course_key
             block_key = BlockKey(usage_key.block_type, usage_key.block_id)
-            source_structure = source_structures.get(src_course_key, [])
+            source_structure = source_structures[src_course_key]
             if block_key not in source_structure['blocks']:
                 raise ItemNotFoundError(usage_key)
             source_block_info = source_structure['blocks'][block_key]